# Mbox Viewer — full site content (English) > Every public page of https://mboxviewerpro.com in this language, as Markdown, in a single file. > 88 pages · generated 2026-09-11 · each page is also available on its own at + index.md --- [Now on the Mac App Store and Microsoft Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) # Read MBOX files on Mac & Windows. Any size. Instantly. Back up your Gmail with Google Takeout and read it offline. Open, search and export emails from MBOX and EML archives — from a few KB to 50+ GB — without your computer breaking a sweat. [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) See how it works ## Mbox Viewer in one minute Recorded on macOS with a sample mailbox. Mbox Viewer is also available for Windows, where the interface differs slightly. [Try the online viewer](https://onlinemboxviewer.com/) macOS 14+ · Apple Silicon · Windows 10/11 and Windows Server macOS Windows ![Mbox Viewer on macOS showing a three-column layout: message list, color-coded Gmail labels in the sidebar and a rendered HTML newsletter.](https://mboxviewerpro.com/_astro/screenshot-mbox-viewer.C55Od4qx_Z15OkrC.webp) No Electron No Java No cloud 100% offline Read-only How to open an MBOX file ## Three steps, on Mac or Windows No import, no conversion, no account. Your file is opened exactly as it is, and left exactly as it was. 1. 1 ### Install Mbox Viewer Free from the Mac App Store or the Microsoft Store. Mailboxes up to 1 GB open without buying anything. 2. 2 ### Open the file Drag it onto the window or double-click it. A Gmail export from Google Takeout, a Thunderbird mailbox and an Apple Mail .mbox folder all open as they are — no conversion step. 3. 3 ### Read it, search it, take what you need The archive is indexed once and re-opens in under a second. Search it, print it, or export the messages you need as EML, PDF or a new MBOX file. [Step by step on Mac →](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/) [Step by step on Windows →](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/) ## Built for one job, done right - 01 ### Your Gmail, offline on your computer Use Google Takeout to back up your entire Gmail account, then read, search and browse it offline — no internet required, no account login. - 02 ### Other tools choke on large files Most MBOX readers crash or freeze past a few hundred MB. Many ship a whole browser or JVM just to show a list of emails. - 03 ### Native, streaming, instant Mbox Viewer streams through files of any size without loading them into memory. Truly native on Mac and Windows. Indexes once, re-opens in under a second. ## Everything you need to live inside your email archive A focused, native toolset — not a web app in a window. ### Handles any size Streaming parser with a 1 MB buffer opens files from a few KB to 50+ GB without loading them into RAM. ### Instant re-opens A binary index with SHA-256 validation makes every re-open take under a second, whatever the file size. ### Powerful search Full query syntax: from:, to:, subject:, body:, date:, has:attachment, size:>, OR, negation and exact phrases. ### Gmail labels Reads Gmail labels straight from Takeout. Browse by label in the sidebar with live message counts. ### Full export Export to EML, CSV, plain text or extract every attachment. Merge multiple MBOX files with dedup. ### Export a selection as MBOX Pick the messages that matter — by search, by label or by hand — and write them to a new mailbox that holds only those. The original file is never touched. ### Conversation threads The JWZ threading algorithm groups messages into conversations with reply chains up to four levels deep. ### Privacy first Everything runs locally. No cloud, no telemetry, no data ever leaves your computer. Strictly read-only. ### Truly native Native on Mac and Windows — dark mode, drag & drop, system share and print. No Electron, no Java. ### Repair damaged mailboxes Deep-scan recovery re-detects lost message boundaries and exports a repaired copy — the original file is never modified. (Pro) ### Export to PDF Export any message to a self-contained, multi-page PDF with the same layout as printing. One message is free; batch export is Pro. ### Export to HTML Save any message as a self-contained HTML file with images embedded and attachments as downloadable links — it opens anywhere. One message is free; batch is Pro. ### Properties, MIME & Hex views Three new ways to inspect a message: a Properties panel, the MIME part tree and a raw hex dump — ideal for technical or forensic work. [See all features](https://mboxviewerpro.com/features/) ## Works with your email client Mbox Viewer reads the standard mbox format — the same format virtually every email client and service uses for exports and backups. If your app can export mbox, Mbox Viewer can open it. No import, no conversion, no account: just open the file. `Mozilla Thunderbird` `Gmail / Google Takeout` `Apple Mail` `Postbox` `Eudora` `Entourage` `Evolution` `Claws Mail` `SeaMonkey` `The Bat!` `Opera Mail` `Sylpheed` `Mutt` `Netscape` `Mozilla Mail` `Spicebird` `PocoMail` `Mulberry` `PowerMail` `Sparrow` `Cone` `GNU Mail` `Outlook for Mac (via converter)` `…and any client that exports standard mbox` Apple Mail and Thunderbird now open directly, with no extra steps. [Have Outlook (PST/OLM)? See how to convert it in our step-by-step guide.](https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/) ![](https://mboxviewerpro.com/_astro/appicon.DZ-pr8RP_ZJ3cFU.png) Your MBOX came from Google Takeout? ## The archive Google sent you holds much more than mail Photos, activity, contacts, calendars, bookmarks — and services that came back empty. Takeout Reports, our free app for Mac and Windows, opens the archive and tells you what's inside, without unzipping it. [Meet Takeout Reports](https://mboxviewerpro.com/takeoutreports/) ## Available in 18 languages Mbox Viewer's interface and user guide are localized into 18 languages, so you can work through your email in the one you know best. - English - Español - Deutsch - Français - Italiano - 日本語 - 한국어 - Nederlands - Polski - Português (BR) - Português (PT) - Русский - Svenska - Dansk - Norsk - Türkçe - 简体中文 - 繁體中文 ## Opens a 50 GB archive in under 5 minutes And re-opens it in under a second — every time, thanks to the binary index. | File size | Messages | First open | Re-open | RAM | | --- | --- | --- | --- | --- | | 500 MB | ~5,000 | < 5 sec | < 1 sec | < 100 MB | | 5 GB | ~50,000 | < 30 sec | < 1 sec | < 200 MB | | 50 GB | ~500,000 | < 5 min | < 1 sec | < 600 MB | ## Free, and Pro when you outgrow it The free version is the whole app, not a demo: no time limit, no watermarks, no nagging. Pro lifts the size limit and adds the heavy-duty jobs — one payment that never expires, or a yearly subscription. ### Free Everything you need to read an archive - Mailboxes up to 1 GB - Full search, Gmail labels and threading - Export to EML, CSV, text and MBOX, and pull out attachments - PDF and HTML of a single message ### Pro For archives that do not fit, and jobs that do not stop at one - No file size limit - Batch export to PDF and HTML - Repair damaged mailboxes - Merge mailboxes of any combined size [See the full comparison](https://mboxviewerpro.com/features/) ## Stop fighting your email backups Free for files up to 1 GB. Unlock unlimited size with an in-app purchase: one payment or a yearly subscription. No account. [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) Buying for a school or an organization? [See the Education edition and volume licensing.](https://mboxviewerpro.com/education/) --- Author # David Carrero Fernández-Baillo Who builds Mbox Viewer and writes the articles and guides on this site. David Carrero Fernández-Baillo develops Mbox Viewer and writes everything published here: the guides, the blog and the glossary. He works from Color Vivo Internet, S.L., the company behind the app on the Mac App Store and the Microsoft Store. The app did not start as an app. It grew out of mboxShell, an open-source terminal tool for reading MBOX files, published on GitHub and still maintained there. Mbox Viewer is the native Mac and Windows version of that same idea, and the two are still developed side by side. One decision shapes the whole product: an email archive is read where it sits. No conversion, no import step, no cloud and no telemetry — the file is opened read-only and left exactly as it was found. Everything written on this site follows from having built the thing that does it. ## What he writes here - [Blog](https://mboxviewerpro.com/blog/) - [Guides](https://mboxviewerpro.com/guides/) ## Elsewhere - [Personal site](https://carrero.es) - [Color Vivo Internet, S.L.](https://colorvivo.com) - [mboxShell on GitHub](https://github.com/dcarrero/mboxshell) --- # Blog News, updates, and ideas from the team behind Mbox Viewer — the native Mac and Windows app for opening MBOX and EML email archives. - [ `mbox` `archives` `product` ## How to Open a 50 GB MBOX File Big MBOX files don't crash readers because they are corrupt — they crash them because most readers load the whole file into memory first. What a streaming parser and an index change, with real numbers. September 11, 2026 Read ](https://mboxviewerpro.com/blog/how-to-open-a-50-gb-mbox-file/) - [ `mbox` `privacy` `archives` ## Is It Safe to Open an MBOX File? An MBOX file is plain text and cannot execute anything by itself. The real risks are elsewhere: attachments you save and open, remote images that report back to the sender, and readers that upload your archive to a server. September 9, 2026 Read ](https://mboxviewerpro.com/blog/is-it-safe-to-open-an-mbox-file/) - [ `announcement` `product` `macos` ## Mbox Viewer 2.8.6 for Mac and Windows: Gmail Labels Stop Being a Wall of Rows Nested Gmail labels now fold into a tree instead of a flat wall of near-identical rows, the annual subscription is back next to the lifetime licence, and Privacy can forget what you have opened. On the Microsoft Store since 4 September and the Mac App Store since the 7th, plus 2.8.7 for Windows. September 7, 2026 Read ](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-8-6-and-2-8-7/) - [ `thunderbird` `mbox` `archives` ## Where Thunderbird Keeps Your Email Thunderbird stores every folder as an MBOX file with no extension, inside a profile folder your system hides. Here is where to find it on Mac, Windows and Linux — and how to read that mail without Thunderbird installed. September 7, 2026 Read ](https://mboxviewerpro.com/blog/where-thunderbird-keeps-your-email/) - [ `mbox` `formats` `pst` ## MBOX Converter: When You Actually Need One Most people searching for an MBOX converter want to read their mail, not convert it — and converting makes a second copy of an archive they already have. Here is when conversion is genuinely the answer, and what to convert to. September 5, 2026 Read ](https://mboxviewerpro.com/blog/mbox-converter-when-you-need-one/) - [ `mbox` `macos` `windows` ## Nothing Happens When You Double-Click an MBOX File Double-clicking a .mbox file does nothing on Windows, and on a Mac it hands the file to Apple Mail, which tries to import it. Here is why neither system knows what to do with your mailbox, and how to fix it in a minute. September 3, 2026 Read ](https://mboxviewerpro.com/blog/double-click-mbox-file-does-nothing/) - [ `mbox` `gmail` `archives` ## How Do You Work With an MBOX File? You asked Google for your data, waited days, and got a file you cannot open. Here is what to actually do with an MBOX file: read it, search it, pull messages out of it, and keep it somewhere it will survive. September 1, 2026 Read ](https://mboxviewerpro.com/blog/how-do-you-work-with-an-mbox-file/) - [ `history` `legacy` `mbox` ## Eudora: The Email Client of the Early Internet, and How to Read Its Mail Today Steve Dorner wrote it in 1988 and named it after a short story. Qualcomm sold it to eighteen million people. It died in 2006, and in 2018 the Computer History Museum published its source code under a BSD licence. If you still have a Eudora folder on an old disk, its mail is in mbox — and it opens today. August 31, 2026 Read ](https://mboxviewerpro.com/blog/eudora-the-email-client-and-its-mbx-files/) - [ `mbox` `formats` `archives` ## What Is an MBOX File? An MBOX file is a plain-text file holding many email messages one after another, each starting with a line that begins "From ". It is what Google Takeout hands you when you export Gmail — and what Thunderbird and Apple Mail keep your mail in. August 30, 2026 Read ](https://mboxviewerpro.com/blog/what-is-an-mbox-file/) - [ `announcement` `product` `macos` ## What's Inside Your Google Takeout? A Free Mac App That Tells You Ten ZIP files of twenty gigabytes each, and no idea what is in them. Takeout Reports opens a Google Takeout archive and reports what it holds — how many messages, how many photos, which years, which services came back empty — without unzipping it and without touching the network. August 28, 2026 Read ](https://mboxviewerpro.com/blog/what-is-inside-your-google-takeout/) - [ `education` `product` `macos` ## MBOX archives for schools and organizations: the edition you buy in Apple School Manager Apple School Manager buys apps, not in-app purchases. That is why Mbox Viewer Pro for Education exists: a Custom App that arrives unlocked, bought by the seat and deployed by MDM. August 26, 2026 Read ](https://mboxviewerpro.com/blog/mbox-viewer-for-schools-and-organizations/) - [ `thunderbird` `mbox` `archives` ## How to Split Large Thunderbird Mailbox Files Without Losing Emails A Thunderbird folder is a single mbox file, and after fifteen years it can weigh more than the disk it started on. Here is how to cut one into smaller mailboxes — with Mbox Viewer or with mboxShell, our open-source terminal tool — and, more importantly, how to prove afterwards that not a single message was lost. August 25, 2026 Read ](https://mboxviewerpro.com/blog/how-to-split-large-thunderbird-mbox-files/) - [ `announcement` `product` `windows` ## Mbox Viewer for Windows 2.8.4 and 2.8.5: Exporting a Selection, and Printing That Finally Says Who Wrote Two updates in two days on the Microsoft Store: 2.8.4 exports your selection as a new MBOX and doubles the free plan to 1 GB; 2.8.5 fixes printing, which had been leaving out the subject, the date and the sender since the very first version. August 24, 2026 Read ](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-8-4-and-2-8-5-windows/) - [ `announcement` `product` `macos` ## What's New in Mbox Viewer 2.8.4 for Mac: Hand Over Only What Has To Be Handed Over Version 2.8.4 exports your selection as a brand-new MBOX, doubles the free plan to 1 GB and brings an edition for schools and universities. On the Mac App Store since 23 August. August 23, 2026 Read ](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-8-4-mac/) - [ `announcement` `product` `macos` ## What's New in Mbox Viewer 2.8.2: Merging Mailboxes, Rebuilt Version 2.8.2 for Mac and Windows is all about merging mailboxes: Apple Mail exports are traceable again, the merge finally tells you what it is doing, and the toolbar explains itself. Still strictly read-only. August 7, 2026 Read ](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-8-2/) - [ `announcement` `product` `macos` ## What's New in Mbox Viewer 2.7.0: Faster, More Private, More Accessible Mbox Viewer 2.7.0 is a big reliability, privacy, accessibility and speed update — faster on large mailboxes, stronger tracking-pixel blocking, full VoiceOver and keyboard support, and rock-solid handling of huge or malformed files. Still strictly read-only. July 3, 2026 Read ](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-7-0/) - [ `formats` `mbox` `pst` ## A Field Guide to Email Storage Formats: History, Anatomy and a Comparison How email is actually stored on disk — MBOX, Maildir, EML, PST, OST, OLM, MSG, NSF and historical formats like Eudora. Their history, how they're built, what each one is good for, and a side-by-side comparison. June 18, 2026 Read ](https://mboxviewerpro.com/blog/email-formats-history-and-anatomy/) - [ `mbox` `eml` `formats` ## MBOX, EML, PST, OLM: Email Archive Formats Explained What's actually inside an email archive? A plain-language tour of the four formats you'll meet — MBOX, EML, PST and OLM — and how to read each one on a Mac. June 11, 2026 Read ](https://mboxviewerpro.com/blog/email-archive-formats-explained/) - [ `mbox` `archives` `legacy` ## Reading Old Email Archives from Eudora, Entourage and Other Classic Clients on a Modern Mac That backup from Eudora, Entourage, Netscape or PowerMail is probably standard mbox — which means a modern Mac can still read it. Here's how to find out and open it safely. June 11, 2026 Read ](https://mboxviewerpro.com/blog/read-old-email-archives-on-modern-mac/) - [ `backup` `gmail` `privacy` ## Why You Should Back Up Your Gmail Locally (and How) Cloud email is convenient until it isn't. Here's why keeping a local Gmail backup matters — account lockouts, accidental deletion, leaving providers — and how Mbox Viewer makes that archive usable. May 26, 2026 Read ](https://mboxviewerpro.com/blog/why-back-up-your-gmail/) - [ `announcement` `product` `macos` ## Introducing Mbox Viewer: Open Any MBOX or EML File, Instantly Why we built Mbox Viewer — a native macOS app that opens MBOX and EML files of any size with streaming performance, total privacy, and no Electron or Java in sight. May 20, 2026 Read ](https://mboxviewerpro.com/blog/introducing-mbox-viewer/) --- # What's new in Mbox Viewer A plain-language history of every release — what changed and why it matters, without the code-level details. [RSS feed](https://mboxviewerpro.com/changelog/rss.xml) macOS Windows ## macOS `Mac App Store` 1. ### v2.8.6 `Latest` September 7, 2026 Gmail labels stop being a wall of rows - New Gmail keeps the hierarchy inside the label name — Work/Clients/Acme is one label, not three — so the sidebar listed every path flat and a mailbox with a real label tree turned into a wall of near-identical rows. They now fold into a tree: each row shows only its last part, with the full path on hover, and the branch holding the label you are filtering by opens on its own. A rung no message actually carries (Work/Clients when only Work/Clients/Acme exists) is drawn greyed and without a count — it groups and unfolds, as in Gmail, but it does not filter by a label nobody has. If no label contains a slash, the sidebar looks exactly as before. - New The annual subscription is on sale again, next to the lifetime licence. The upgrade screen shows both cards and you choose: pay once, or pay yearly. Either unlocks the same thing, and nothing changes for anyone who already bought the lifetime licence. The subscription card is only drawn when the store hands the app a real price for it, so where it is not on sale the screen is the one you already know. The free tier still opens mailboxes up to 1 GB with every feature. - Improved Settings › General › Privacy can now forget which files have been opened. The app keeps a bookmark per opened mailbox so it can reach the file again after a restart, and those bookmarks are keyed by full path — together they are a list of the mailboxes you have opened. A third button drops them all; nothing breaks, because the next time you open a file its bookmark is created again. The section also spells out now that everything it lists stays on this Mac and that clearing cannot be undone. And clearing the search history finally clears it: every open window kept its own copy in memory and wrote it back on the next search, so what you had just cleared came straight back. - Fixed Every link the app opens now points at mboxviewerpro.com — the website in About and Help, the privacy policy, and the App Store listing's marketing, support and privacy URLs — and it opens the page in your own language instead of sending everyone to the English one. On the way, a real bug: the privacy policy link opened a 404 in Spanish, French, German and Portuguese, because the app built the URL as /es/privacy/ while the site translates the address too (/es/privacidad/, /fr/confidentialite/, /de/datenschutz/). Those four now reach the real page, and Polish was added alongside them. (Version 2.8.5 was Windows-only, which is why the Mac line jumps from 2.8.4 to 2.8.6: from here on the same number means the same thing on both platforms.) 2. ### v2.8.4 August 23, 2026 A new mailbox with only what has to be handed over - New Export your selection as a new MBOX. Pick the messages that matter — by search, by Gmail label or by hand — and the app writes them into a brand-new mailbox that contains only those. It is the delivery step of a legal hold or a public-records request: narrow a huge archive down to what actually has to be handed over, and produce a file with exactly that in it. The original archive is never modified. - Improved The free plan goes from 500 MB to 1 GB. Same app, same features, no time limit — just twice the room before you need Pro. - New And there is now a separate edition for schools, universities and organizations: Mbox Viewer Pro for Education, the same app with everything unlocked permanently, bought by the seat in Apple School Manager or Apple Business Manager and deployed by MDM — no in-app purchases, no licence keys, no accounts and nothing that expires. [Mbox Viewer Pro for Education](https://mboxviewerpro.com/education/) 3. ### v2.8.3 August 20, 2026 A review prompt that waits until the app has earned it - New The app can now ask for an App Store review — quietly, and only after it has earned it. The system prompt appears once you have finished at least three real jobs (an export, a repaired mailbox or a merge), never in the first three days after installing, at most once per version and no more often than every 120 days. It waits for a moment when the window is in front and no sheet is open, so it never lands on top of the dialog that just finished. - New Help → Rate Mbox Viewer Pro… opens the store listing whenever you feel like leaving a review, without waiting to be asked. Mac App Store version only: outside the store the app neither counts anything nor shows anything. 4. ### v2.8.2 August 7, 2026 Merging mailboxes, rebuilt - Fixed Merging Apple Mail mailboxes tagged every message with the same origin. Apple Mail's "Export Mailbox…" writes a folder named "Inbox.mbox" containing a file called literally "mbox", so the optional X-Mbox-Source header recorded "mbox" for all of them — losing the whole point of the option, which is knowing which archive an email came from. Merged messages now carry the name you recognize, and mailboxes that would share a name are told apart by their folder. - Improved Merging no longer requires opening a mailbox first. It is now an app-level action with its own window, available from File → Merge MBOX Files… and from a button on the welcome screen. If a mailbox is already open, it starts out in the list. - Improved The merge window is far more usable: the list scrolls instead of pushing the window off-screen, shows each mailbox's size and a total, accepts mailboxes dropped onto it, and reports real progress while it works ("Merging 2 of 5 — Inbox.mbox"). When it finishes it tells you how it went in your own language and offers Show in Finder, Open Merged Mailbox and Close. - Improved The toolbar explains itself. Conversation threading no longer shares an icon with Search Filters — it now uses the conversation bubbles Mail.app uses for the same thing — and the six icon-only view segments (Text, Full Headers, Properties, MIME, Raw, Hex) name themselves on hover, shortcut included: "Full Headers (⌘2)". - Fixed Menu items that need an open mailbox — File → Export, the View and Message commands, Search Filters — are greyed out with none open, instead of looking available and being silently ignored when clicked. 5. ### v2.8.1 July 17, 2026 The search field no longer disappears while you type - Fixed The search field no longer vanishes from the toolbar while you type. At certain window widths, entering a query could push it out of view with no way to bring it back until you resized the window. It now keeps a fixed width; the match count is still shown in the status bar. - Fixed ⌘F now always leads somewhere: if the search field can't be focused, it opens the Search Filters panel instead of doing nothing. 6. ### v2.8.0 July 13, 2026 Export to PDF and HTML, repair damaged mailboxes, and new inspection views - New Export any message to PDF. The exported PDF keeps the same layout as printing, in a self-contained multi-page file. Exporting one message is free; batch PDF export (several at once) is a Pro feature. - New Export any message to a self-contained HTML file — headers, body with inline images embedded, and attachments included as downloadable links — so it opens anywhere with no external references. Single-message export is free; batch export is Pro. - New New attachments pane: a gallery that lists every attachment with a per-type icon, its content type and size, image preview and one-click save — including “Save all” to a folder. - New Three new ways to inspect a message, alongside Text and Headers: a Properties view (all addresses, dates and threading identifiers, selectable and copyable), a MIME structure view (the message's part tree with content types, encoding, charset and sizes) and a Hex view (an offset · hex · ASCII dump of the raw message) — ideal for technical or forensic inspection. - New Repair damaged mailboxes (Pro). When a mailbox opens empty or as one giant message, its “From ” separators were probably lost; a deep-scan recovery re-detects the message boundaries. You can rebuild the view in place or export a brand-new, repaired .mbox copy — and the original file is never modified (the app stays strictly read-only). - Improved Merge mailboxes with full traceability: a new option adds an “X-Mbox-Source” header to each merged message with its origin file name, so a combined archive still shows which mailbox every email came from. Off by default, and it works with or without duplicate removal. 7. ### v2.7.1 July 4, 2026 Merge Mailboxes fixes and a 1 GB free limit - Fixed The “Merge Mailboxes” picker no longer greys out your mailboxes: you can now select any recognizable mailbox — including extensionless Thunderbird mailboxes (INBOX, Sent…), .mbs/.mbx archives, files on a NAS, and Apple Mail “Name.mbox” export folders. - New Merging up to 1 GB of combined mailboxes is free; larger merges are now a Pro feature, shown with a clear notice and an upgrade option. 8. ### v2.7.0 July 3, 2026 Faster, more private, more accessible - Improved Faster on large mailboxes: quicker searching, lower memory use, and no more UI freezes when opening very large messages or exporting. - Security More private: remote images (tracking pixels) are blocked more thoroughly, temporary files are cleaned up automatically, and new Settings let you clear your search history and index cache. - Improved More accessible: full VoiceOver and keyboard support, adjustable message text size and font, better contrast, and the in-app language picker now lists all 18 languages. - Fixed More robust: handles malformed or oversized MBOX/EML files gracefully instead of freezing or crashing, and export/merge failures are now clearly reported. - New HTML messages now show the sender header and quick actions (Export, Print, Share) at the top, just like plain-text messages. 9. ### v2.6.5 June 18, 2026 Full Headers view and 8 new languages - New New Full Headers view: see the complete header block (From, To, Cc, Date, Message-ID, Reply-To and more) in a clean, read-only pane. Pick it from the toolbar (Text / Headers / Raw) or from View → Full Headers (⌘2). Thanks to Verender Badial for the suggestion. - New Eight new languages — Simplified Chinese, Traditional Chinese, Turkish, Swedish, Danish, Norwegian, Russian and European Portuguese — bringing the app to 18 languages. 10. ### v2.6.0 June 16, 2026 Apple Mail and Thunderbird exports open directly - New Apple Mail export folders (.mbox packages) now open directly — no need to dig out the inner “mbox” file. - New Mailbox files without an extension — like Thunderbird's INBOX or Sent — open directly, no renaming to .mbox required. 11. ### v2.5.0 June 15, 2026 Safer HTML and smarter search - Security Email HTML is now sanitized before display — scripts, iframes and other active content are stripped, on top of the existing remote-image blocking. - Improved Free-text search now looks inside message bodies too, not just subject and sender — so a plain word finds everything. - Fixed Hardened parsing of very large files so a message split across read buffers can never inflate the message count. 12. ### v2.4.1 June 2, 2026 Accurate version info and code redemption - Fixed The About window now always shows the real installed version. - New Added a «Redeem Code» button so you can use Mac App Store promo codes for the Pro upgrade. 13. ### v2.4.0 May 31, 2026 Pro is now a simple one-time purchase - Improved Streamlined the App Store edition to a single lifetime Pro unlock. The upgrade screen now loads its price instantly. 14. ### v2.3.0 March 16, 2026 Clearer upgrade path - New Added an «Upgrade to Pro» banner on the welcome screen so unlocking unlimited file size is one tap away. - Fixed Several refinements to the purchase and restore flow. 15. ### v2.2.0 March 8, 2026 New Window shortcut and legal links - New Added a New Window command (Cmd+N) and quick links to the Privacy Policy and Terms. - Improved Clicking the Dock icon with no windows open now reopens the welcome window. 16. ### v2.1.0 February 23, 2026 Mbox Viewer arrives on the Mac App Store - New First Mac App Store release, with sandboxing and automatic updates through the App Store. - Fixed Resolved several export and save-panel issues for a smoother experience. 17. ### v1.1.0 February 13, 2026 Now speaking ten languages - New Added German, French, Italian, Japanese, Korean, Dutch, Polish and Brazilian Portuguese — full UI and user guide. 18. ### v1.0.0 February 12, 2026 Mbox Viewer 1.0 — the first release - New Streaming MBOX and EML reader that opens files of any size without loading them into memory, with an instant-reopen binary index. - New Powerful search syntax, Gmail labels, conversation threading, and export to EML, CSV, text and attachments. - New Fully native macOS app — SwiftUI + AppKit, dark mode, Drag & Drop, Quick Look, Share and Print. ## Windows `Microsoft Store` 1. ### v2.8.7 `Latest` September 4, 2026 Two ways to have Pro, and the texts now say so - Fixed Settings no longer tells someone who pays the subscription that “Pro Lifetime” is active — it just says Pro is active. The licence state now knows which of the two plans Pro is running on, and when both are present the lifetime one wins, because that is the one you cannot lose. The text is decided in a single place, so it also comes out right in the refresh that runs right after buying, not only when you open Settings. - Improved On the paywall, the one-time card now reads “One payment, forever” and no longer adds “— no subscription”, which is redundant right next to the subscription card. The full wording still shows when the annual plan is not on sale and there is only one option. 2. ### v2.8.6 September 4, 2026 The label sidebar becomes a tree - New Gmail exports Work/Clients/Acme as one label, hierarchy and all, and the sidebar listed those paths flat — a mailbox with a real tree became a wall of near-identical rows. A customer asked for this before buying. Each row now shows only its last part, with the full path in the tooltip; branches fold and unfold, and the one holding the label you are filtering by opens on its own. A rung that exists only as a prefix — Work/Clients/Acme exists but nothing is labelled Work/Clients — is greyed and has no count: it groups, but it does not filter, as in Gmail. If no label contains a slash, the sidebar looks exactly as before. - New The annual subscription is on sale again, next to Pro Lifetime. The paywall shows both cards and you choose; the lifetime licence is still a single payment and does not expire. The annual card only appears if the Store returns a price for it, so where it is not on sale the screen is the one you already know. Either unlocks the same thing, and whoever already bought the lifetime licence notices no change. - Improved Settings → Privacy can now clear the search history, which is the only thing the app keeps about your mail: the indexes live in memory and there is no recent-files list. It is also a single list for the whole app now — each tab used to carry its own copy and the last one to search overwrote the others, so clearing would not have cleared anything. - Fixed The name offered when exporting a selection as MBOX no longer eats the end of the file name. A Google Groups mailbox is named after the group (my-group@googlegroups.com) and the app offered my-group@googlegroups-selection.mbox; the extension is now stripped only when it really is a mailbox one (.mbox, .eml, .mbs, .mbx). Two more fixes came out of verifying the tree on Windows: folding the branch that held the active label used to drop the filter silently, and opening a branch could move the selection. - Improved The product site is now mboxviewerpro.com. The links in About — website, support and privacy — point at the new domain and open the page in the language you are using the app in: the site translates the address of each page too (/es/privacidad/, not /es/privacy/), and where there is no translated version the English one opens. The old address redirects, so nothing you had saved stops working. 3. ### v2.8.5 August 24, 2026 Printing an email now carries its header - Fixed Printing an email left out the subject, the date and who it was from and to. Ctrl+P sent the message body to the printer on its own — the app draws those fields in the interface, next to the body, where the print engine never sees them — so the page began mid-message. On a forwarded email the headers of the quoted message did come out, which made it look as though only the first one was missing. Printing now produces the same document as "Export → To PDF…": subject, From, To, Cc and date at the top, separated from the body, and the attachment list at the foot. It is a Windows-only defect, there since the first version; macOS never had it. - Improved Ctrl+P opens the email as a PDF in your system viewer, and you print from there — with a real preview of what will come out of the printer, and the option to save the file or pass it on. Until now that was handwork: export to PDF, find the file, open it. It is one step now. The content stays as sealed off as it is on screen: no JavaScript and not a single network request, printing included. - Fixed Messages with no subject can be printed too. The button checked the subject to decide whether a message was selected, so with an empty one it did nothing at all. 4. ### v2.8.4 August 23, 2026 A new mailbox with only what has to be handed over - New Export your selection as a new MBOX. Pick the messages that matter — by search, by Gmail label or by hand — and the app writes them into a brand-new mailbox that contains only those. It is the delivery step of a legal hold or a public-records request: narrow a huge archive down to what actually has to be handed over, and produce a file with exactly that in it. The original archive is never modified. - Improved The free plan goes from 500 MB to 1 GB. Same app, same features, no time limit — just twice the room before you need Pro. 5. ### v2.8.3 August 20, 2026 A review prompt that waits until the app has earned it - New The app can now ask for a Microsoft Store review — quietly, and only after it has earned it. The store's own dialog appears once you have finished at least three real jobs (an export, a merge or a repaired mailbox), never in the first three days after installing, at most once per version and no more often than every 120 days. It waits for a moment when the window is in front with no dialog open, and if it cannot find one within about 30 seconds it leaves it for next time. - New About → "Rate Mbox Viewer Pro" opens the store listing on its reviews section whenever you feel like leaving one, without waiting to be asked (and with a web fallback if the Store app is unavailable). Outside the Store the app neither counts anything nor shows anything. - Fixed Dialogs got cut off in short windows. With the window around 570 px tall, the About box was clipped and its rate link was left half-visible: Windows does not limit a dialog's content to the height of its window. About, Help, Statistics and the upgrade screen now measure the real window when they open, cap their content there and scroll inside it, adjusting again if you resize the window while the dialog is up. 6. ### v2.8.2 August 8, 2026 Traceable merges, with real progress and an explanation - Fixed Merging mailboxes exported from Apple Mail tagged every message with the same origin. Apple Mail exports each mailbox as a folder named "Inbox.mbox" containing a file called literally "mbox" — and that inner file is the one the app opens, so the X-Mbox-Source header recorded "mbox" everywhere and the combined archive lost the traceability the header exists for. It now records the name you recognize, and mailboxes that would share a name are told apart by their folder ("Work/Inbox.mbox"). - Improved Merging shows real progress and says where the file ended up. The bar used to be indeterminate with a fixed label even though the engine reports progress; it now names each mailbox as it goes ("Merging 2 of 5: Inbox.mbox", the same name that gets written into the header), and when it finishes the status bar shows the full path of the merged file — before, you only saw its name in the tab. - Improved Every toolbar control now has a tooltip. Fifteen of them had no explanation at all — the search box, the sort dropdown, the three welcome-screen buttons, the eight viewer tabs and the two buttons on each attachment — and Export and Print now show their shortcut (Ctrl+E / Ctrl+P). - Improved The Help now explains merging and the source-mailbox header. A new "Merge mailboxes" section covers how merging works, what "Remove duplicates" does, what the X-Mbox-Source checkbox writes and how to see that header in a message (the Headers tab). The checkbox's own help text said "the source file name"; it now says "mailbox", which is what it actually writes. - Fixed "Repair mailbox" and "Export repaired copy" are no longer dead clicks. In the settings menu they were always enabled, but with no mailbox loaded in the active tab they did nothing and said nothing; they are now disabled until they can work. Merge stays available, because it works with or without an open mailbox. 7. ### v2.8.0 July 12, 2026 Export to PDF and HTML, repair damaged mailboxes, and new inspection views - New Export any message to PDF. The exported PDF keeps the same layout as printing, in a self-contained multi-page file. Exporting one message is free; batch PDF export (several at once) is a Pro feature. - New Export any message to a self-contained HTML file — headers, body with inline images embedded, and attachments included as downloadable links — so it opens anywhere with no external references. Single-message export is free; batch export is Pro. - New New attachments pane: a gallery that lists every attachment with a per-type icon, its content type and size, image preview and one-click save — including “Save all” to a folder. - New Three new ways to inspect a message, alongside Text and Headers: a Properties view (all addresses, dates and threading identifiers, selectable and copyable), a MIME structure view (the message's part tree with content types, encoding, charset and sizes) and a Hex view (an offset · hex · ASCII dump of the raw message) — ideal for technical or forensic inspection. - New Repair damaged mailboxes (Pro). When a mailbox opens empty or as one giant message, its “From ” separators were probably lost; a deep-scan recovery re-detects the message boundaries. You can rebuild the view in place or export a brand-new, repaired .mbox copy — and the original file is never modified (the app stays strictly read-only). - Improved Merge mailboxes with full traceability: a new option adds an “X-Mbox-Source” header to each merged message with its origin file name, so a combined archive still shows which mailbox every email came from. Off by default, and it works with or without duplicate removal. 8. ### v2.7.1 July 4, 2026 Merge from settings, safer viewer and a more reliable engine - New Combine mailboxes right from the settings (⚙) menu — including the mailbox you already have open. Merging up to 1 GB combined is free; Pro unlocks larger merges. - Improved More reliable: merging never leaves a corrupted file, message dates display more accurately, and very large or damaged mailboxes are handled safely. - Security Stronger security: the email viewer now blocks all remote and local-network content (tracking pixels and file/UNC links), preventing information leaks. 9. ### v2.7.0 June 19, 2026 More formats, sort by recipient and safer HTML - New Open more mailbox formats: Apple Mail, Thunderbird, and .mbs/.mbx files — plus a new “Open folder…” command and folder drag-and-drop. - New New “Sort by recipient (To)” option in the message list. - Security Stronger security: email HTML is now sanitized before it is displayed (scripts and remote content are blocked). - Fixed Various improvements and fixes. 10. ### v2.6.5 June 18, 2026 Mbox Viewer arrives on Windows - New A native Windows app (WinUI) is coming to the Microsoft Store, built on the same streaming engine that opens MBOX and EML files of any size — up to 50 GB — without loading them into memory. - New Feature parity with the Mac app: powerful search, Gmail labels, conversation threading, export to EML/CSV/text, 18 languages and the same Free / Pro one-time purchase. 11. ### v1.0 `Not public` June 1, 2026 Windows port begins in the lab - New We start building the native Windows port: a WinUI 3 app (Windows App SDK) written in C# 12 / .NET 8, with WebView2 (Edge Chromium) rendering the email HTML in isolation. - New It reuses the same streaming approach as the Mac app — opening huge MBOX/EML files without loading them into memory — and will ship as an MSIX package on the Microsoft Store, with the Pro unlock via Windows.Services.Store. --- # Why choose Mbox Viewer? How it stacks up against Electron- or Java-based MBOX readers and generic utilities. | What matters | Mbox Viewer | Electron / Java readers | Generic utilities | | --- | --- | --- | --- | | 50 GB+ files | Yes, streaming | Often crashes | Rarely | | Instant re-open | < 1 sec (index) | Re-parses each time | Varies | | Memory usage | < 600 MB | High | Medium | | Native app | Mac & Windows | Bundled browser | Depends | | Gmail labels | Yes | Sometimes | No | | 100% offline / private | Yes, read-only | Varies | Varies | | Export to EML/CSV/text | All + attachments | Limited | Limited | [Download and see for yourself](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- `Volume licensing programme` # Mbox Viewer Pro for Education The same app your team already knows, with every Pro feature unlocked permanently — bought by the seat in Apple School Manager or Apple Business Manager and deployed by MDM. It is a programme for organizations, not a product you buy with a button. [Request access](#request) - Custom App · Apple School / Business Manager - No in-app purchases - No licence keys, no accounts - Works fully offline ## Why this edition exists In the App Store, Mbox Viewer Pro unlocks with an in-app purchase. Apple School Manager and Apple Business Manager can buy and assign apps, but not in-app purchases — so an IT department has no way to buy that unlock for every Mac in a district and hand it out. A Custom App is Apple's standard answer to exactly that: a separate, private build of the app that ships already unlocked, so there is nothing for the end user to activate and nothing for IT to explain in a manual. The long version is on the blog: [MBOX archives for schools and organizations](https://mboxviewerpro.com/blog/mbox-viewer-for-schools-and-organizations/) ## What the licence includes ### Everything unlocked, permanently Every Pro feature is available from the first launch, with no file size limit. Nothing expires. ### No purchases, keys or accounts The user opens the app and it works. There is no in-app purchase to hide, no licence key to distribute and no sign-in to support. ### MDM deployment, reassignable seats Push it like any other app from your MDM. If someone leaves, the seat goes back to the pool and can be assigned to another person. ### Add seats whenever you need them More seats are bought from Apple School or Business Manager at any time, without contacting us again. ### No server, no analytics, no cloud The app works completely offline: email data never leaves the Mac. For a school district this is usually the deciding point. ### Native, sandboxed, universal Universal binary for Apple silicon and Intel, inside Apple's sandbox, macOS 14 or later. No Electron, no Java runtime to maintain. ## Who it is for School districts, universities, public administrations and companies that already run Apple School Manager or Apple Business Manager with an MDM — Jamf, Intune, Mosyle, Kandji, Addigy or any other. If your organization does not use either of them, write to us anyway and we will see what can be done. ### What organizations use it for - #### eDiscovery, legal holds and public-records requests Review a large Google Vault or Google Takeout export, search it down to the messages the request actually covers, and export exactly those as a new MBOX mailbox. The original export is never modified — everything you excluded is simply not in the new file. - #### Mailboxes of people who have left Open the exported mailbox of a former employee or student when there is no live account behind it any more. - #### Historical archives and old servers Dig through old backups and mail-server copies that no current client can open any more. ## Price 39.99 USD per seat One payment per seat, below the 44.99 USD lifetime licence in the App Store. No subscription, no renewal, no expiry date. That is the price for the United States. Apple sets every other territory by automatic conversion from the base price, so an organization in the euro area sees 44.99 €, and a Canadian one its own equivalent. The exact amount your organization pays is the one shown in Apple School or Business Manager. ## How to request it ### There is no buy button here — on purpose A Custom App is private: it has no public App Store listing, and it only becomes visible to an organization once we have added that organization's Apple School or Business Manager Organization ID to its record. So the first step is not a payment — it is telling us who you are, so we can put your ID on the list. 1. 01 ### You write to us With your organization's name, its Apple School or Business Manager Organization ID, roughly how many seats you need and a contact person. The Organization ID is in Apple School or Business Manager, under Settings → Enrollment Information. 2. 02 ### We register your Organization ID We add it to the app record, on the build that is already published: no new version and nothing for you to install. Apple then takes up to 24 hours to make the app visible in your account, and we email you when it is there. 3. 03 ### The app appears in your account We email you when it is ready. In Apple School or Business Manager you will find it under Apps and Books → Custom Apps. 4. 04 ### You buy the seats and deploy them The purchase happens inside Apple School or Business Manager, with your usual payment method, and the seats are assigned through your MDM. You can buy more at any time. ## Request access for your organization Four fields and we can start. We only use what you send here to register your organization and reply to you. ## Questions IT departments ask ### Do we need Apple School Manager or Apple Business Manager? Yes. It is the only channel Apple provides for buying and deploying a Custom App. If your organization uses neither, write to us anyway and we will look at what can be done. ### Do users have to sign in or activate anything? No. The app arrives unlocked and opens ready to work. ### Do the licences expire? No. One payment per seat, and it stays yours. ### Can we reassign a licence? Yes, from Apple School or Business Manager, like any other app you have bought there. ### Is any email data sent anywhere? No. The app has no server and no analytics, and it works offline. Nothing leaves the Mac. ### Can we buy more seats later? Yes, at any time and without contacting us: once your Organization ID is registered, the app stays in your Custom Apps list. ### Can it redact content inside a message? No, and it is worth being precise about it: the app removes messages from the set, not text from inside a message. If a responsive email contains a paragraph that has to be blacked out before it goes out, that is a different tool. If the job is deciding which messages are responsive and producing a file containing only those, that is exactly what this does. ### Does it modify our files? No. It is strictly read-only: same size and same modification date after opening them. ## Not an organization? For a single Mac, the regular app in the Mac App Store is the same program: free to try, with a one-time in-app purchase to remove the size limit. [Get it on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [See all features](https://mboxviewerpro.com/features/) --- # Frequently asked questions Everything about MBOX files, Thunderbird and Google Takeout exports, Apple Mail archives and how Mbox Viewer works. ## What is an MBOX file? MBOX is a standard format for storing email messages in a single file. Google Takeout exports your Gmail as MBOX, and many email clients and servers use it for backups and archives. ## How do I back up my Gmail as MBOX? Go to takeout.google.com, deselect everything, select only “Mail”, and create the export. Google prepares a .zip archive (it can take hours for large accounts). Download it, unzip it, and open the .mbox file with Mbox Viewer. ## Can it open very large files? Yes. Mbox Viewer uses a streaming parser that never loads the whole file into memory, so it opens archives of 50 GB and beyond. The first open builds an index; every later open is under a second. ## Does it modify my MBOX file? Never. Mbox Viewer is strictly read-only. It creates a small index file next to your MBOX for fast access, but never writes to the original. ## What's the difference between Free and Pro? Free includes every reading tool — search, Gmail labels, threading, the MIME and hex views — and is limited to mailboxes up to 1 GB. Pro lifts that limit and adds three things: batch export to PDF and HTML, repairing damaged mailboxes, and merges above 1 GB combined. Export to EML, CSV, text and MBOX, and pulling out attachments, work the same in both. Pro is a one-time in-app purchase. [See the full comparison](https://mboxviewerpro.com/features/) ## Is there a subscription? Yes, but it is optional. Pro comes two ways inside the app, on the Mac App Store or the Microsoft Store: one payment that never expires, or a yearly subscription. Either unlocks exactly the same features. No account, and no recurring charge if you pick the one-time payment. ## Does it support HTML emails? Yes. Mbox Viewer renders HTML emails with their original formatting. For privacy, remote images are blocked by default, with an option to load them, and message HTML is sanitized before display. ## Which macOS versions are supported? macOS 14 Sonoma and later. It's a Universal Binary that runs natively on Apple Silicon (M1–M4) and Intel Macs. ## Is there a Windows version? Yes. A native Windows app is available on the Microsoft Store, with the same features as the Mac app — including 18 languages and files up to 50 GB. ## Does my data leave my Mac? No. Everything runs locally — no cloud, no telemetry, no account. Your emails never leave your machine. ## How do I open a Thunderbird mbox file on Mac? Thunderbird stores each mailbox (Inbox, Sent…) as a standard mbox file without a file extension. Mbox Viewer opens these extensionless mailboxes directly — just point it at the file in your Thunderbird profile folder, no renaming to .mbox needed. Files exported with add-ons like ImportExportTools NG already carry the extension and open the same way. ## How do I open an Apple Mail export (.mbox folder)? Apple Mail exports a folder named “YourMailbox.mbox” that contains a file called simply “mbox”. Mbox Viewer opens the .mbox export package directly — just select (or drag & drop) the “YourMailbox.mbox” folder and it finds the messages inside automatically. No need to dig out the inner “mbox” file. ## Can I view my Gmail / Google Takeout export? Yes. Google Takeout delivers your Gmail as a standard .mbox file that Mbox Viewer opens directly — including your Gmail labels, which show up in the sidebar. Unzip the Takeout archive and open the .mbox file inside. ## Can I open Outlook emails (PST / OLM)? Not directly — Outlook stores mail in PST/OLM, which isn't mbox. Convert the file to mbox with a converter tool first, then open the result with Mbox Viewer. ## Can a school or a company buy licences in volume? Yes, through a separate edition: Mbox Viewer Pro for Education, a Custom App bought by the seat in Apple School Manager or Apple Business Manager and deployed by MDM, with everything unlocked and no in-app purchase. It is not on the public App Store: an organization is added by its Organization ID first. [Mbox Viewer Pro for Education](https://mboxviewerpro.com/education/) ## I double-clicked my MBOX file and nothing happened. Why? Because macOS and Windows ship with no app registered for the .mbox extension, so the double-click has nowhere to go — or it hands the file to Apple Mail, which tries to import it instead of opening it. Installing Mbox Viewer registers the extension: from then on a double-click opens the mailbox for reading, without importing it anywhere. ## Can I save emails from an MBOX file as PDF? Yes. Any message can be printed or saved as PDF with its headers intact, and Pro does it in batches for a whole selection. You can also export messages as EML, as plain text, as CSV, or as a brand-new MBOX file containing only what you picked. ## Is it safe to open an MBOX file? An MBOX file is plain text, so it cannot run anything by itself; the risk lives in what you do with what is inside — an attachment you save and open, or a remote image that tells a sender you read the message. Mbox Viewer is read-only and never writes to your archive, and it blocks remote images by default, so nothing loads from the internet unless you ask for it. ## How big can an MBOX file get before it stops opening? There is no ceiling in the format itself, and none in the app: a 50 GB archive of around half a million messages opens in under five minutes and re-opens in under a second, using less than 600 MB of RAM. What most other readers hit is their own limit, not the file's — they load the whole thing into memory before showing anything. The free version opens mailboxes up to 1 GB; Pro removes that limit. ## Still have a question? [Support](https://mboxviewerpro.com/support/) Download our apps [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- # A complete, native MBOX toolkit Everything you need to open, search, read and export huge email archives on Mac and Windows — without a web app in a window. See how it works ## Mbox Viewer in one minute Recorded on macOS with a sample mailbox. Mbox Viewer is also available for Windows, where the interface differs slightly. ## Built for scale ### Any file size A streaming parser with a 1 MB buffer opens files from a few KB to 50+ GB without ever loading them into RAM. ### Instant re-opens A binary index with SHA-256 validation makes every re-open take under a second, regardless of size. ### Low memory footprint Even a 50 GB archive stays under 600 MB of RAM thanks to on-demand streaming and an LRU message cache. ### Repair damaged mailboxes Deep-scan recovery re-detects lost message boundaries and exports a repaired copy — the original file is never modified. (Pro) ## Find anything ### Powerful search syntax Use from:, to:, subject:, body:, date:, has:attachment, size:>, OR, negation and exact phrases — or the visual filter sheet. ### Gmail labels Reads Gmail labels straight from Takeout. Browse by label in the sidebar with live message counts. ### Conversation threading The JWZ algorithm groups messages into conversations with visual reply chains up to four levels deep. ### Properties, MIME & Hex views Three new ways to inspect a message: a Properties panel, the MIME part tree and a raw hex dump — ideal for technical or forensic work. ## Get your data out ### Export anywhere Export to EML, CSV (Excel-ready, UTF-8 with BOM) or plain text, and extract attachments in bulk. ### Export a selection as a new MBOX Narrow a huge archive down by search, by Gmail label or by hand, and write the result to a brand-new mailbox that contains only those messages — the delivery step of a legal hold or a public-records request. The original file is never modified. ### Merge & dedupe MBOX Combine multiple MBOX files into one, with optional Message-ID deduplication. Export a single label as its own MBOX. ### Attachments View attachments inline, preview with Quick Look (Spacebar), save individually or in bulk, or drag straight to Finder (Explorer on Windows). ### Export to PDF Export any message to a self-contained, multi-page PDF with the same layout as printing. One message is free; batch export is Pro. ### Export to HTML Save any message as a self-contained HTML file with images embedded and attachments as downloadable links — it opens anywhere. One message is free; batch is Pro. ## Native & private ### Truly native on Mac & Windows Native on Mac (SwiftUI + AppKit) and Windows (WinUI). Dark mode, drag & drop, system share, print and full keyboard navigation. No Electron, no Java. ### Privacy by design Everything runs locally. No cloud, no telemetry, no account. Remote images blocked and HTML sanitized by default. ### Drag & Drop everywhere Drop MBOX or EML files onto the app to open them, and drag messages out as .eml or attachments to Finder. ## Search syntax at a glance Combine prefixes, operators and exact phrases to pinpoint any message.
from:from:john@example.comMessages from this sender
to:to:team@Sent to this address
subject:subject:"quarterly report"Subject contains phrase
body:body:invoiceFull-text body search
has:attachmenthas:attachmentMessages with attachments
label:label:ImportantGmail label
date:date:2024-03From a given month
size:>size:>5mbLarger than a size
--spamExclude a term
ORfrom:alice OR from:bobEither condition
## Available in 18 languages Mbox Viewer's interface and user guide are localized into 18 languages, so you can work through your email in the one you know best. - English - Español - Deutsch - Français - Italiano - 日本語 - 한국어 - Nederlands - Polski - Português (BR) - Português (PT) - Русский - Svenska - Dansk - Norsk - Türkçe - 简体中文 - 繁體中文 ## Free vs Pro, line by line Same app, same interface, same 18 languages. Pro is not a different program: it is these four things. | What you can do | Free | Pro from $44.99 one-time · from $8.99 per year | | --- | --- | --- | | Maximum mailbox size | 1 GB | Unlimited | | Search, Gmail labels and conversation threads | | | | Export to EML, CSV, plain text and MBOX | | | | Extract attachments in bulk | | | | Properties, MIME tree and hex views | | | | Export to PDF and HTML | One message | In batches | | Merge mailboxes with deduplication | Up to 1 GB combined | Unlimited | | Repair damaged mailboxes | | | Pro is bought inside the app, on the Mac App Store or the Microsoft Store, and comes two ways: one payment that never expires, or a yearly subscription. Either unlocks exactly the same features. No account and no licence key. Prices are a guide and show the lower of the two stores. Each store sets its own and charges in your currency, so the final amount depends on your country and the taxes that apply there. [Pricing by country](https://mboxviewerpro.com/pricing/). [Try it on your own archive](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- # Email & MBOX glossary Key terms for email archives, formats, protocols and the anatomy of a message — each with its own page, explained in plain language. [File formats](#formats) [Protocols & services](#protocols) [Message structure](#structure) [Encoding & charsets](#encoding) [Concepts & features](#concepts) ## File formats [ MBOX .mbox · mbox file · mailbox file A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ EML A single-message file in MIME format, containing headers, body, and attachments. EML files are widely supported across email clients and are useful for archiving or sharing individual messages. ](https://mboxviewerpro.com/glossary/eml/)[ MSG Microsoft Outlook's proprietary binary format for a single email message, storing headers, body, and attachments in a Compound Document Structure. Unlike EML, MSG is not a plain-text standard. ](https://mboxviewerpro.com/glossary/msg/)[ PST OST Personal Storage Table — Microsoft Outlook's container file for an entire mailbox, including folders, messages, contacts, and calendar items. Also known as OST when used for offline sync with Exchange or Microsoft 365. ](https://mboxviewerpro.com/glossary/pst/)[ Maildir A mailbox format that stores each email message as a separate file within a directory hierarchy, rather than concatenating all messages into a single file like MBOX. ](https://mboxviewerpro.com/glossary/maildir/)[ MBX (Eudora) TOC · Eudora Eudora's mailbox file: plain mbox under a different extension, paired with a .toc index file. Readable today with no conversion — but its attachments were stored outside the mailbox. ](https://mboxviewerpro.com/glossary/mbx/)[ OLM The archive format Outlook for Mac exports to — a proprietary container that is not the same thing as Windows' PST, and that few other programs can read without conversion. ](https://mboxviewerpro.com/glossary/olm/)[ EMLX Apple Mail Apple Mail's per-message file format: one message per file, prefixed by its byte length and followed by an XML property list of Apple's own metadata. ](https://mboxviewerpro.com/glossary/emlx/) ## Protocols & services [ IMAP Internet Message Access Protocol — the standard protocol for accessing email stored on a server, keeping messages synchronized across multiple devices without downloading and deleting them. ](https://mboxviewerpro.com/glossary/imap/)[ POP3 Post Office Protocol 3 — an older email retrieval protocol that downloads messages from a server to a local device, typically removing them from the server afterward. ](https://mboxviewerpro.com/glossary/pop3/)[ SMTP Simple Mail Transfer Protocol — the standard protocol used to send and relay email messages between mail servers. It is used for outgoing mail only; reading email requires IMAP or POP3. ](https://mboxviewerpro.com/glossary/smtp/)[ Google Takeout Google's official service for exporting your personal data, including Gmail. For email, it produces one or more MBOX files containing all your messages and their Gmail labels. ](https://mboxviewerpro.com/glossary/google-takeout/)[ Google Vault Google Workspace's retention and eDiscovery tool. An administrator can hold, search and export the mail of accounts across an organisation — and the export is MBOX. ](https://mboxviewerpro.com/glossary/google-vault/)[ Gmail labels labels Gmail's tagging system that assigns one or more labels to each message, serving the role that folders play in traditional email clients. A single message can carry multiple labels simultaneously. ](https://mboxviewerpro.com/glossary/gmail-labels/) ## Message structure [ Header The structured metadata block at the beginning of an email message, containing fields like From, To, Subject, Date, and numerous technical fields that describe how the message was composed, routed, and encoded. ](https://mboxviewerpro.com/glossary/header/)[ MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. ](https://mboxviewerpro.com/glossary/mime/)[ Multipart boundary A MIME message structure that combines multiple content parts — such as plain text, HTML, and attachments — in a single message, each separated by a unique boundary string. ](https://mboxviewerpro.com/glossary/multipart/)[ Message-ID A globally unique identifier assigned to each email message, specified in the Message-ID header. It is used to track messages, build conversation threads, and detect duplicates when merging archives. ](https://mboxviewerpro.com/glossary/message-id/)[ In-Reply-To / References Email headers (In-Reply-To and References) that link a reply to the message it responds to, enabling mail clients and archive tools to group related messages into conversation threads. ](https://mboxviewerpro.com/glossary/in-reply-to/)[ Envelope The delivery metadata used by SMTP servers to route an email message — specifically the envelope sender (MAIL FROM) and envelope recipients (RCPT TO) — which may differ from the visible From and To headers. ](https://mboxviewerpro.com/glossary/envelope/)[ Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. ](https://mboxviewerpro.com/glossary/attachment/)[ Inline image CID An image embedded directly into an HTML email body using a Content-ID (cid:) reference, rather than attached as a separate downloadable file. The image data is stored as a MIME part within the same message. ](https://mboxviewerpro.com/glossary/inline-image/)[ mboxrd / mboxo From-quoting · mboxcl2 The MBOX family's variants, which differ in how they protect body lines that begin with "From ". mboxrd escapes them reversibly; mboxo does not; mboxcl and mboxcl2 use a Content-Length header instead. ](https://mboxviewerpro.com/glossary/mboxrd/)[ Received The header each mail server adds as a message passes through it. Read from the bottom up, the Received lines reconstruct the route a message actually travelled. ](https://mboxviewerpro.com/glossary/received/)[ SPF, DKIM and DMARC SPF · DKIM · DMARC The three mechanisms that establish whether a message really came from the domain it claims: SPF authorises sending servers, DKIM signs the message cryptographically, and DMARC ties the two to a published policy. ](https://mboxviewerpro.com/glossary/dkim/) ## Encoding & charsets [ Charset The character encoding that specifies how bytes in a text part are mapped to readable characters. Common charsets include UTF-8, ISO-8859-1, and Shift\_JIS; a mismatch causes garbled text known as mojibake. ](https://mboxviewerpro.com/glossary/charset/)[ Base64 A binary-to-text encoding scheme that represents arbitrary binary data using only 64 printable ASCII characters, widely used in email to safely transmit attachments and binary content. ](https://mboxviewerpro.com/glossary/base64/)[ Quoted-printable A MIME transfer encoding that represents text with mostly ASCII characters, escaping non-ASCII bytes as =XX hex sequences. It keeps the majority of the text human-readable in the raw message source. ](https://mboxviewerpro.com/glossary/quoted-printable/)[ Encoded-word (RFC 2047) RFC 2047 An encoding scheme defined in RFC 2047 ("Encoded-Word") that allows non-ASCII characters in email header fields such as Subject and From, by encoding them as =?charset?encoding?text?= tokens. ](https://mboxviewerpro.com/glossary/rfc2047/) ## Concepts & features [ Threading (JWZ) The process of grouping related email messages into conversations by following In-Reply-To and References header links, typically using the JWZ algorithm that supports up to four levels of nesting. ](https://mboxviewerpro.com/glossary/threading/)[ Deduplication The process of detecting and removing duplicate email messages from an archive, typically by comparing Message-ID values, to avoid redundancy when merging multiple MBOX files. ](https://mboxviewerpro.com/glossary/deduplication/)[ Streaming parser A parsing technique that reads a file incrementally in small chunks rather than loading the entire file into memory at once, enabling tools to open and index very large MBOX files — tens or hundreds of gigabytes — with low memory usage. ](https://mboxviewerpro.com/glossary/streaming-parser/)[ Binary index A compact index file that Mbox Viewer writes alongside an MBOX archive after the first parse, storing message byte offsets and metadata to enable near-instant reopens without re-scanning the entire file. ](https://mboxviewerpro.com/glossary/binary-index/)[ HTML email An email message whose body is formatted with HTML and CSS, allowing rich typography, layout, colors, and images. Most modern email is HTML, but privacy and security considerations require careful rendering. ](https://mboxviewerpro.com/glossary/html-email/)[ Universal Binary A macOS application bundle that contains native compiled code for both Apple Silicon (ARM64) and Intel (x86\_64) architectures, running natively on either processor without emulation. ](https://mboxviewerpro.com/glossary/universal-binary/)[ App Sandbox App Sandbox is a macOS security feature that restricts an application's access to system resources, files, and network connections, limiting the potential impact if the app or its dependencies have a vulnerability. ](https://mboxviewerpro.com/glossary/sandbox/)[ eDiscovery legal hold · disclosure The legal process of identifying, preserving, reviewing and handing over electronic records — email above all. It is the reason most people ever need to cut a mailbox down to a specific set of messages. ](https://mboxviewerpro.com/glossary/ediscovery/)[ Compacting X-Mozilla-Status The operation that actually removes deleted messages from an mbox file. Until it runs, a deleted message is only marked as deleted — it is still in the file, and still readable. ](https://mboxviewerpro.com/glossary/compacting/) --- # Guides & Tutorials Step-by-step guides for working with MBOX and EML email archives on Mac and Windows: Gmail exports, huge files, Apple Mail and Thunderbird. - [ Tutorial ## How to Export Gmail with Google Takeout (and Open It on Mac) A step-by-step guide to exporting your Gmail to an MBOX file with Google Takeout, downloading it safely, and opening it instantly in Mbox Viewer on macOS. May 12, 2026 Read ](https://mboxviewerpro.com/guides/how-to-export-gmail-with-google-takeout/) - [ Tutorial ## How to Open an MBOX File on Mac (Even Huge Ones) Three ways to open an MBOX file on macOS — Apple Mail, Thunderbird or a dedicated viewer — with the steps for each, and which one to pick for a multi-gigabyte Gmail archive. May 15, 2026 Read ](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/) - [ Tutorial ## How to Convert MBOX to CSV, EML, and Text (and Extract Attachments) A practical guide to exporting an MBOX file into CSV spreadsheets, individual EML messages, plain text, and PDF — plus how to extract every attachment in bulk — using Mbox Viewer on Mac. May 18, 2026 Read ](https://mboxviewerpro.com/guides/convert-mbox-to-csv-and-eml/) - [ Tutorial ## Mbox Viewer Search Syntax Cheat Sheet A complete reference for searching MBOX and EML archives in Mbox Viewer: from:, to:, subject:, body:, date:, has:attachment, size:>, OR, negation, and exact phrases — with copy-ready examples. May 21, 2026 Read ](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/) - [ Tutorial ## How to Open a Thunderbird MBOX File on Mac Thunderbird stores your mail in standard mbox files — they just have no extension. Here are two easy ways to read them on macOS with Mbox Viewer, without importing anything. June 11, 2026 Read ](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-mac/) - [ Tutorial ## How to Open an Apple Mail Export (.mbox Folder) on Mac Apple Mail exports a .mbox folder with a file named “mbox” inside — that file is your mail in standard mbox format. Here's how to export from Mail and read the result with Mbox Viewer. June 11, 2026 Read ](https://mboxviewerpro.com/guides/how-to-open-apple-mail-export-on-mac/) - [ Tutorial ## How to Open an MBOX File on Windows 10 and 11 Three ways to open and read an MBOX file on Windows: import it into Thunderbird, open it with a dedicated viewer, or take a quick look. Steps for each, and which one fits your file. June 18, 2026 Read ](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/) - [ Tutorial ## How to Open a Thunderbird MBOX File on Windows Thunderbird on Windows stores your mail as standard mbox files with no extension, tucked inside your profile folder. Here's how to find and read them with Mbox Viewer on Windows 10 and 11. June 18, 2026 Read ](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-windows/) - [ Tutorial ## How to Open a Gmail (Google Takeout) MBOX File on Windows Downloaded your Gmail with Google Takeout and got a giant .mbox inside a ZIP? Here's how to unzip it on Windows and open the mailbox with Mbox Viewer — no import, no Gmail login. June 18, 2026 Read ](https://mboxviewerpro.com/guides/how-to-open-gmail-takeout-mbox-on-windows/) - [ Tutorial ## How to Open an Apple Mail Export (.mbox) on Windows Moving from Mac to PC? Apple Mail exports a .mbox package that looks like a folder on Windows. Here's how to find the real mailbox inside it and read it with Mbox Viewer. June 18, 2026 Read ](https://mboxviewerpro.com/guides/how-to-open-apple-mail-export-on-windows/) - [ Tutorial ## How to Convert Outlook PST/OLM to MBOX (Mac & Windows) Outlook stores mail in PST (Windows) or OLM (Mac), which Mbox Viewer can't open directly. Here's how to convert PST and OLM files to standard mbox — free, step by step — then read them. June 18, 2026 Read ](https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/) --- # mboxShell The free terminal tool behind Mbox Viewer. Open, search and export MBOX files of any size — right from your shell, on Linux, macOS, FreeBSD and Windows. `Latest v0.7.3` `Free & open source` `Written in Rust` `MIT` [View source on GitHub](https://github.com/dcarrero/mboxshell) [Downloads & releases](https://github.com/dcarrero/mboxshell/releases) mboxshell ![mboxShell running in a terminal, showing an MBOX archive with its message list, folders and reading pane.](https://mboxviewerpro.com/_astro/screenshot-mboxshell.Ba4cJsaI_2wUWfS.webp) ## A full MBOX toolkit in your terminal Everything you need to work with huge email archives — reading, searching, threading and exporting — with no GUI and no cloud. ### Any file size A streaming parser with a 1 MB buffer opens 50 GB+ Gmail Takeout backups while keeping RAM around 500 MB. ### Sub-second re-opens A persistent binary index — verified with SHA-256 — reopens even the largest archive in under a second. ### Field-based search Filter with from:, subject:, date:, body:, has:attachment and label:, plus exact phrases and an OR that groups alternatives: a OR b c reads as (a OR b) AND c — in the TUI or from the command line. ### Gmail labels & Google Groups Detects X-Gmail-Labels and turns them into virtual folders you can browse and filter by. In a Google Takeout archive, each Groups mailbox appears under its own group name. ### Conversation threading Groups related messages into conversations with the classic JWZ threading algorithm, using Google's own conversation id (X-GM-THRID) when the mailbox carries one. ### Export anywhere Save messages as MBOX, EML, CSV, TXT or HTML, and extract attachments individually or in bulk. ### Merge & dedupe Combine several MBOX files into one, with optional deduplication so nothing is imported twice. ### Full terminal UI A ratatui-based TUI with three layout modes, vi-style navigation and shell completions for bash, zsh, fish, PowerShell and elvish. ### Cross-platform & bilingual A single ~5 MB binary with no runtime dependencies. Runs on Linux, macOS, FreeBSD and Windows, with an English/Spanish interface. ## What's new The three most recent releases. The latest, v0.7.3, shipped on September 4, 2026. ### v0.7.3 September 4, 2026 The Mac app moved to a new domain - Documentation only: both READMEs and both manuals still pointed at mboxviewer.net, the former domain of the macOS app. They now name mboxviewerpro.com, and so does the repository's own project link. [Release notes v0.7.3](https://github.com/dcarrero/mboxshell/releases/tag/v0.7.3) ### v0.7.2 August 22, 2026 Export a selection as a new mailbox - export --format mbox writes the selected messages into a single new MBOX. Until now a selection could leave as .eml, CSV, text or HTML — a folder of files — but never as a mailbox again, so there was no way to hand over part of an archive in the format it arrived in. Together with --query that is the whole delivery flow: filter a large dump (a Google Vault export, a Takeout archive) down to the messages that actually belong in the handover, and produce a mailbox holding only those. - A message read out of an MBOX is copied byte for byte, keeping its own From envelope line and whatever quoting the source used: rewriting the envelope could only corrupt an archive that was already valid. One with no envelope line — because it came from an EML — gets one synthesized, plus > quoting of body lines that start with From, without which the result is not a readable mailbox. The output is committed by temp file and rename, like the merge, so a failure halfway through never leaves a half-written mailbox under the name you asked for, and the source file is never touched. 7 new tests (241 in total). [Release notes v0.7.2](https://github.com/dcarrero/mboxshell/releases/tag/v0.7.2) ### v0.7.1 August 20, 2026 Search queries that mean what you wrote - OR now has a precedence. It used to be a flag on the whole query, so a single OR anywhere turned every term into an alternative: from:alice OR from:bob subject:invoice did not mean "either sender, about invoices" — it returned everything from alice, everything from bob and everything whose subject said invoice, whoever sent it. On a 6,787-message mailbox that is the difference between 49 hits and 2,102. A query is now a list of AND-ed groups, each group a list of OR-ed terms, and OR is what puts two terms in the same group: a OR b c reads as (a OR b) AND c. There are still no parentheses. - after:X before:Y was impossible to express. The query held a single date filter, so the second one silently replaced the first and only before: survived — half of what you typed was dropped without a word. Date and size filters now accumulate, which also turns size:>1mb size:<5mb into a real band. - after: now includes its own day and before: still excludes its own, so after:2024-01-01 before:2025-01-01 is exactly the year 2024 — the half-open reading Gmail's operators use, and consistent with date:A..B, which was already inclusive. Both manuals and both READMEs document the precedence rule and the date bounds. 23 new tests (234 in total). [Release notes v0.7.1](https://github.com/dcarrero/mboxshell/releases/tag/v0.7.1) [Read the full changelog](https://github.com/dcarrero/mboxshell/blob/main/CHANGELOG.md) ## One command away mboxshell $ mboxshell archive.mbox # Open the interactive terminal UI $ mboxshell search archive.mbox "from:jane has:attachment" # Search straight from the command line $ mboxshell export archive.mbox -f eml -o out/ # Export messages to MBOX, EML, CSV, TXT or HTML $ mboxshell merge a.mbox b.mbox -o all.mbox --source-header # Merge files — duplicates removed by default (--no-dedup to keep them), noting which mailbox each message came from $ mboxshell attachments archive.mbox -o files/ # Extract every attachment at once ### Install it Grab a pre-built binary for Linux, macOS, FreeBSD or Windows from the releases page, or build it yourself with Cargo: ``` $ cargo install --git https://github.com/dcarrero/mboxshell.git ``` ## The open-source engine behind Mbox Viewer Mbox Viewer for Mac and Windows grew out of mboxShell. The app wraps the same idea — reading MBOX files of any size, fully offline — in a polished native interface with search, labels, threading and EML support. Prefer the terminal? mboxShell is free and MIT-licensed. [Get it on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) [github.com/dcarrero/mboxshell](https://github.com/dcarrero/mboxshell) --- # Free online MBOX viewer Open and read MBOX email archives right in your browser. Nothing is uploaded — your file never leaves your device. 100% private — runs entirely in your browser, nothing is uploaded. [Open the online viewer](https://onlinemboxviewer.com/) Free · no signup · opens in a new tab ## Bigger files or more features? The online viewer is for a quick look at small archives. For files of any size, search, labels and EML support, get the native macOS app. [Get it on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- # Pricing by country Mbox Viewer is free to download and stays free for mailboxes up to 1 GB, with every feature. Pro lifts that limit, and it is bought inside the app: one payment that never expires, or a yearly subscription — either unlocks exactly the same thing. Below is what each store charges in every market where the app is sold. 243 of 243 markets | Country or region | Mac App Store One-time | Mac App Store Per year | Microsoft Store One-time | Microsoft Store Per year | | --- | --- | --- | --- | --- | | Afghanistan | $44.99 | $8.99 | $49.99 | $9.99 | | Åland Islands | — | — | $49.99 | $9.99 | | Albania | $49.99 | $9.99 | $49.99 | $9.99 | | Algeria | $44.99 | $8.99 | DZD 5,399.00 | DZD 1,099.00 | | American Samoa | — | — | $49.99 | $9.99 | | Andorra | — | — | €49.99 | €9.99 | | Angola | $44.99 | $8.99 | $49.99 | $9.99 | | Anguilla | $44.99 | $8.99 | $49.99 | $9.99 | | Antarctica | — | — | $49.99 | $9.99 | | Antigua & Barbuda | $44.99 | $8.99 | $49.99 | $9.99 | | Argentina | $44.99 | $8.99 | ARS 714.00 | ARS 142.00 | | Armenia | $49.99 | $9.99 | $49.99 | $9.99 | | Aruba | — | — | $49.99 | $9.99 | | Australia | A$69.99 | A$14.99 | A$74.95 | A$14.95 | | Austria | €49.99 | €9.99 | €49.99 | €9.99 | | Azerbaijan | $49.99 | $9.99 | $49.99 | $9.99 | | Bahamas | $49.99 | $9.99 | $49.99 | $9.99 | | Bahrain | $49.99 | $9.99 | BHD 19.000 | BHD 3.800 | | Bangladesh | — | — | BDT 3,899.00 | BDT 779.00 | | Barbados | $49.99 | $9.99 | $49.99 | $9.99 | | Belarus | $49.99 | $9.99 | $49.99 | $9.99 | | Belgium | €49.99 | €9.99 | €49.99 | €9.99 | | Belize | $44.99 | $8.99 | $49.99 | $9.99 | | Benin | $49.99 | $9.99 | $49.99 | $9.99 | | Bermuda | $44.99 | $8.99 | $49.99 | $9.99 | | Bhutan | $44.99 | $8.99 | $49.99 | $9.99 | | Bolivia | $44.99 | $8.99 | $49.99 | $9.99 | | Bosnia & Herzegovina | €49.99 | €9.99 | $49.99 | $9.99 | | Botswana | $44.99 | $8.99 | $49.99 | $9.99 | | Bouvet Island | — | — | $49.99 | $9.99 | | Brazil | R$299.90 | R$59.90 | R$184.95 | R$36.95 | | British Indian Ocean Territory | — | — | $49.99 | $9.99 | | British Virgin Islands | $44.99 | $8.99 | $49.99 | $9.99 | | Brunei | $44.99 | $8.99 | $49.99 | $9.99 | | Bulgaria | €49.99 | €9.99 | BGN 103.00 | BGN 20.00 | | Burkina Faso | $44.99 | $8.99 | $49.99 | $9.99 | | Burundi | — | — | $49.99 | $9.99 | | Cambodia | $49.99 | $9.99 | $49.99 | $9.99 | | Cameroon | $49.99 | $9.99 | $49.99 | $9.99 | | Canada | CA$59.99 | CA$11.99 | CA$63.99 | CA$12.79 | | Cape Verde | $44.99 | $8.99 | $49.99 | $9.99 | | Caribbean Netherlands | — | — | $49.99 | $9.99 | | Cayman Islands | $44.99 | $8.99 | $49.99 | $9.99 | | Central African Republic | — | — | $49.99 | $9.99 | | Chad | $44.99 | $8.99 | $49.99 | $9.99 | | Chile | CLP 49,990 | CLP 9,990 | CLP 33,999 | CLP 6,799 | | China | CN¥298.00 | CN¥58.00 | CN¥354.00 | CN¥71.00 | | Christmas Island | — | — | $49.99 | $9.99 | | Cocos (Keeling) Islands | — | — | $49.99 | $9.99 | | Colombia | COP 199,900.00 | COP 39,900.00 | COP 152,900.00 | COP 30,900.00 | | Comoros | — | — | $49.99 | $9.99 | | Congo - Brazzaville | — | $8.99 | $49.99 | $9.99 | | Congo - Kinshasa | $44.99 | $8.99 | $49.99 | $9.99 | | Cook Islands | — | — | $49.99 | $9.99 | | Costa Rica | $44.99 | $8.99 | CRC 26,750.00 | CRC 5,250.00 | | Côte d’Ivoire | $49.99 | $9.99 | $49.99 | $9.99 | | Croatia | €49.99 | €9.99 | €54.99 | €10.99 | | Curaçao | — | — | $49.99 | $9.99 | | Cyprus | €49.99 | €9.99 | €49.99 | €9.99 | | Czechia | CZK 1,190.00 | CZK 249.00 | CZK 1,429.00 | CZK 289.00 | | Denmark | DKK 399.00 | DKK 79.00 | DKK 399.00 | DKK 80.00 | | Djibouti | — | — | $49.99 | $9.99 | | Dominica | $44.99 | $8.99 | $49.99 | $9.99 | | Dominican Republic | $44.99 | $8.99 | $49.99 | $9.99 | | Ecuador | $44.99 | $8.99 | $49.99 | $9.99 | | Egypt | EGP 2,499.99 | EGP 499.99 | EGP 445.00 | EGP 89.00 | | El Salvador | $44.99 | $8.99 | $49.99 | $9.99 | | Equatorial Guinea | — | — | $49.99 | $9.99 | | Eritrea | — | — | $49.99 | $9.99 | | Estonia | €49.99 | €9.99 | €49.99 | €9.99 | | Eswatini | $44.99 | $8.99 | $49.99 | $9.99 | | Ethiopia | — | — | $49.99 | $9.99 | | Falkland Islands | — | — | $49.99 | $9.99 | | Faroe Islands | — | — | $49.99 | $9.99 | | Fiji | $44.99 | $8.99 | $49.99 | $9.99 | | Finland | €49.99 | €9.99 | €49.99 | €9.99 | | France | €49.99 | €9.99 | €49.99 | €9.99 | | French Guiana | — | — | $49.99 | $9.99 | | French Polynesia | — | — | $49.99 | $9.99 | | French Southern Territories | — | — | $49.99 | $9.99 | | Gabon | $44.99 | $8.99 | $49.99 | $9.99 | | Gambia | $44.99 | $8.99 | $49.99 | $9.99 | | Georgia | $49.99 | $9.99 | $49.99 | $9.99 | | Germany | €49.99 | €9.99 | €49.99 | €9.99 | | Ghana | $49.99 | $9.99 | $49.99 | $9.99 | | Gibraltar | — | — | $49.99 | $9.99 | | Greece | €49.99 | €9.99 | €49.99 | €9.99 | | Greenland | — | — | $49.99 | $9.99 | | Grenada | $44.99 | $8.99 | $49.99 | $9.99 | | Guadeloupe | — | — | $49.99 | $9.99 | | Guam | — | — | $49.99 | $9.99 | | Guatemala | $44.99 | $8.99 | GTQ 434.00 | GTQ 86.00 | | Guernsey | — | — | $49.99 | $9.99 | | Guinea | — | — | $49.99 | $9.99 | | Guinea-Bissau | $44.99 | $8.99 | $49.99 | $9.99 | | Guyana | $44.99 | $8.99 | $49.99 | $9.99 | | Haiti | — | — | $49.99 | $9.99 | | Heard & McDonald Islands | — | — | $49.99 | $9.99 | | Honduras | $44.99 | $8.99 | $49.99 | $9.99 | | Hong Kong SAR China | HK$368.00 | HK$68.00 | HK$389.00 | HK$78.00 | | Hungary | HUF 19,990.00 | HUF 3,990.00 | HUF 17,300.00 | HUF 3,500.00 | | Iceland | $49.99 | $9.99 | ISK 4,699 | ISK 939 | | India | ₹4,999.00 | ₹999.00 | ₹2,724.00 | ₹549.00 | | Indonesia | — | IDR 149,000.00 | IDR 655,000.00 | IDR 130,000.00 | | Iraq | $44.99 | $8.99 | IQD 55,500 | IQD 11,000 | | Ireland | €49.99 | €9.99 | €49.99 | €9.99 | | Isle of Man | — | — | $49.99 | $9.99 | | Israel | — | ₪29.90 | ₪188.00 | ₪37.50 | | Italy | €49.99 | €9.99 | €49.99 | €9.99 | | Jamaica | $44.99 | $8.99 | $49.99 | $9.99 | | Japan | ¥7,000 | ¥1,500 | ¥5,850 | ¥1,150 | | Jersey | — | — | $49.99 | $9.99 | | Jordan | $44.99 | $8.99 | JOD 48.000 | JOD 9.500 | | Kazakhstan | KZT 24,990.00 | KZT 4,990.00 | KZT 16,800.00 | KZT 3,400.00 | | Kenya | $49.99 | $9.99 | KES 5,850.00 | KES 1,150.00 | | Kiribati | — | — | $49.99 | $9.99 | | Kosovo | €49.99 | €9.99 | — | — | | Kuwait | $44.99 | $8.99 | KWD 15.000 | KWD 3.000 | | Kyrgyzstan | $49.99 | $9.99 | $49.99 | $9.99 | | Laos | $49.99 | $9.99 | $49.99 | $9.99 | | Latvia | €49.99 | €9.99 | €49.99 | €9.99 | | Lebanon | $44.99 | $8.99 | LBP 91,000 | LBP 18,250 | | Lesotho | — | — | $49.99 | $9.99 | | Liberia | $44.99 | $8.99 | $49.99 | $9.99 | | Libya | $44.99 | $8.99 | $49.99 | $9.99 | | Liechtenstein | — | — | CHF 51.50 | CHF 10.00 | | Lithuania | €49.99 | €9.99 | €49.99 | €9.99 | | Luxembourg | €49.99 | €9.99 | €49.99 | €9.99 | | Macao SAR China | $44.99 | $8.99 | $49.99 | $9.99 | | Madagascar | $44.99 | $8.99 | $49.99 | $9.99 | | Malawi | $44.99 | $8.99 | $49.99 | $9.99 | | Malaysia | MYR 199.90 | MYR 39.90 | MYR 194.00 | MYR 39.00 | | Maldives | $44.99 | $8.99 | $49.99 | $9.99 | | Mali | $44.99 | $8.99 | $49.99 | $9.99 | | Malta | €49.99 | €9.99 | €49.99 | €9.99 | | Marshall Islands | — | — | $49.99 | $9.99 | | Martinique | — | — | $49.99 | $9.99 | | Mauritania | $44.99 | $8.99 | MRO 15,599 | MRO 3,099 | | Mauritius | $49.99 | $8.99 | $49.99 | $9.99 | | Mayotte | — | — | $49.99 | $9.99 | | Mexico | MX$999.00 | MX$199.00 | MX$879.00 | MX$177.00 | | Micronesia | $44.99 | $8.99 | $49.99 | $9.99 | | Moldova | $49.99 | $9.99 | $49.99 | $9.99 | | Monaco | — | — | €49.99 | €9.99 | | Mongolia | $44.99 | $8.99 | $49.99 | $9.99 | | Montenegro | €39.99 | €7.99 | €49.99 | €9.99 | | Montserrat | $44.99 | $8.99 | $49.99 | $9.99 | | Morocco | — | $8.99 | MAD 694.00 | MAD 139.00 | | Mozambique | $44.99 | $8.99 | $49.99 | $9.99 | | Myanmar (Burma) | $44.99 | $8.99 | $49.99 | $9.99 | | Namibia | $44.99 | $8.99 | $49.99 | $9.99 | | Nauru | $44.99 | $8.99 | $49.99 | $9.99 | | Nepal | $49.99 | $9.99 | $49.99 | $9.99 | | Netherlands | €49.99 | €9.99 | €49.99 | €9.99 | | New Caledonia | — | — | $49.99 | $9.99 | | New Zealand | NZ$79.99 | NZ$14.99 | NZ$72.90 | NZ$14.50 | | Nicaragua | $44.99 | $8.99 | $49.99 | $9.99 | | Niger | $44.99 | $8.99 | $49.99 | $9.99 | | Nigeria | NGN 69,900.00 | NGN 14,900.00 | NGN 10,499.00 | NGN 2,099.00 | | Niue | — | — | $49.99 | $9.99 | | Norfolk Island | — | — | $49.99 | $9.99 | | North Macedonia | $44.99 | $8.99 | $49.99 | $9.99 | | Northern Mariana Islands | — | — | $49.99 | $9.99 | | Norway | NOK 599.00 | NOK 99.00 | NOK 514.00 | NOK 104.00 | | Oman | $44.99 | $8.99 | OMR 19.500 | OMR 3.900 | | Pakistan | PKR 11,900.00 | PKR 2,500.00 | PKR 5,249.00 | PKR 1,049.00 | | Palau | $44.99 | $8.99 | $49.99 | $9.99 | | Palestinian Territories | — | — | $49.99 | $9.99 | | Panama | $44.99 | $8.99 | $49.99 | $9.99 | | Papua New Guinea | $44.99 | $8.99 | $49.99 | $9.99 | | Paraguay | $44.99 | $8.99 | $49.99 | $9.99 | | Peru | PEN 199.90 | PEN 39.90 | PEN 167.50 | PEN 33.50 | | Philippines | ₱2,990.00 | ₱599.00 | ₱2,300.00 | ₱460.00 | | Pitcairn Islands | — | — | $49.99 | $9.99 | | Poland | PLN 199.99 | PLN 39.99 | PLN 229.99 | PLN 45.99 | | Portugal | €49.99 | €9.99 | €49.99 | €9.99 | | Qatar | QAR 149.99 | QAR 29.99 | QAR 182.50 | QAR 36.50 | | Réunion | — | — | $49.99 | $9.99 | | Romania | RON 249.99 | RON 49.99 | RON 249.99 | RON 49.99 | | Russia | RUB 3,990.00 | RUB 799.00 | $49.99 | $9.99 | | Rwanda | $44.99 | $8.99 | $49.99 | $9.99 | | Samoa | — | — | $49.99 | $9.99 | | San Marino | — | — | €49.99 | €9.99 | | São Tomé & Príncipe | $44.99 | $8.99 | $49.99 | $9.99 | | Saudi Arabia | SAR 199.99 | SAR 39.99 | SAR 186.50 | SAR 37.50 | | Senegal | $49.99 | $9.99 | $49.99 | $9.99 | | Serbia | €49.99 | €9.99 | RSD 6,449 | RSD 1,299 | | Seychelles | $44.99 | $8.99 | $49.99 | $9.99 | | Sierra Leone | $44.99 | $8.99 | $49.99 | $9.99 | | Singapore | SGD 59.98 | SGD 12.98 | SGD 72.00 | SGD 14.40 | | Sint Maarten | — | — | $49.99 | $9.99 | | Slovakia | €49.99 | €9.99 | €49.99 | €9.99 | | Slovenia | €49.99 | €9.99 | €49.99 | €9.99 | | Solomon Islands | $44.99 | $8.99 | $49.99 | $9.99 | | Somalia | — | — | $49.99 | $9.99 | | South Africa | ZAR 999.99 | ZAR 199.99 | ZAR 839.00 | ZAR 169.00 | | South Georgia & South Sandwich Islands | — | — | $49.99 | $9.99 | | South Korea | ₩77,000 | ₩12,000 | ₩62,900 | ₩12,400 | | Spain | €49.99 | €9.99 | €49.99 | €9.99 | | Sri Lanka | $44.99 | $8.99 | $49.99 | $9.99 | | St. Barthélemy | — | — | $49.99 | $9.99 | | St. Helena | — | — | $49.99 | $9.99 | | St. Kitts & Nevis | $44.99 | $8.99 | $49.99 | $9.99 | | St. Lucia | $44.99 | $8.99 | $49.99 | $9.99 | | St. Martin | — | — | $49.99 | $9.99 | | St. Pierre & Miquelon | — | — | $49.99 | $9.99 | | St. Vincent & Grenadines | $44.99 | $8.99 | $49.99 | $9.99 | | Suriname | $49.99 | $9.99 | $49.99 | $9.99 | | Svalbard & Jan Mayen | — | — | $49.99 | $9.99 | | Sweden | SEK 599.00 | SEK 119.00 | SEK 499.00 | SEK 99.00 | | Switzerland | CHF 40.00 | CHF 8.00 | CHF 51.50 | CHF 10.00 | | Taiwan | NT$1,490.00 | NT$290.00 | NT$1,699.00 | NT$339.00 | | Tajikistan | $49.99 | $9.99 | $49.99 | $9.99 | | Tanzania | TZS 129,900.00 | TZS 24,900.00 | $49.99 | $9.99 | | Thailand | THB 1,490.00 | THB 299.00 | THB 1,759.00 | THB 349.00 | | Timor-Leste | — | — | $49.99 | $9.99 | | Togo | — | — | $49.99 | $9.99 | | Tokelau | — | — | $49.99 | $9.99 | | Tonga | $44.99 | $8.99 | $49.99 | $9.99 | | Trinidad & Tobago | $44.99 | $8.99 | TTD 330.00 | TTD 66.00 | | Tunisia | $44.99 | $8.99 | TND 139.000 | TND 28.000 | | Türkiye | TRY 2,499.99 | TRY 499.99 | TRY 141.25 | TRY 28.75 | | Turkmenistan | $44.99 | $8.99 | $49.99 | $9.99 | | Turks & Caicos Islands | $44.99 | $8.99 | $49.99 | $9.99 | | Tuvalu | — | — | $49.99 | $9.99 | | U.S. Outlying Islands | — | — | $49.99 | $9.99 | | U.S. Virgin Islands | — | — | $49.99 | $9.99 | | Uganda | $49.99 | $9.99 | $49.99 | $9.99 | | Ukraine | $49.99 | $9.99 | UAH 1,285.00 | UAH 250.00 | | United Arab Emirates | AED 179.99 | AED 34.99 | $49.99 | $9.99 | | United Kingdom | £44.99 | £8.99 | £41.74 | £8.39 | | United States | $44.99 | $8.99 | $49.99 | $9.99 | | Uruguay | $44.99 | $8.99 | $49.99 | $9.99 | | Uzbekistan | $49.99 | $9.99 | $49.99 | $9.99 | | Vanuatu | $44.99 | $8.99 | $49.99 | $9.99 | | Vatican City | — | — | €49.99 | €9.99 | | Venezuela | $44.99 | $8.99 | $49.99 | $9.99 | | Vietnam | ₫1,299,000 | ₫299,000 | ₫1,109,900 | ₫219,900 | | Wallis & Futuna | — | — | $49.99 | $9.99 | | Western Sahara | — | — | $49.99 | $9.99 | | Yemen | $44.99 | $8.99 | $49.99 | $9.99 | | Zambia | $49.99 | $9.99 | $49.99 | $9.99 | | Zimbabwe | $49.99 | $9.99 | $49.99 | $9.99 | The final price is set by each store, not by us. What you see here is what the App Store and the Microsoft Store published on 4 September 2026; a store can adjust its prices for exchange rates or taxes at any time, and what you are charged depends on the country of your account and the taxes that apply there. Treat this table as a guide: the amount that counts is the one the store shows you at checkout. [See what Pro unlocks](https://mboxviewerpro.com/features/) --- Last updated: August 2026 # Privacy Policy Mbox Viewer and Takeout Reports (“the Apps”) are developed by Color Vivo Internet, S.L. This policy explains how we handle your data in both apps and on this website. ## Local processing Mbox Viewer processes all email files entirely on your machine. No content, metadata or attachments are transmitted to any server. Your files never leave your computer. Takeout Reports works the same way with your Google Takeout archive: it reads each file inside the ZIP, without extracting it, and it has no network access permission at all, on either platform. ## Index files The App creates small binary index files next to your MBOX files for fast access. They are stored locally and never transmitted anywhere. ## Purchases Upgrading to Pro is an in-app purchase through the Mac App Store (or the Microsoft Store on Windows). Apple or Microsoft handles payment; we never receive or store your payment details. We run no license-validation server. Takeout Reports is free and has no in-app purchases. ## Analytics and tracking Neither Mbox Viewer nor Takeout Reports includes analytics, telemetry or tracking. We collect no usage data or crash reports. ## Contact form If you write to us from the support page or from the Mbox Viewer Pro for Education page, we receive what you fill in — your name, email and message, plus your organization's name, its Organization ID and the estimated seats in the case of Education — to reply and handle your request. The email also carries technical details of the connection it was sent from: IP address, browser, language, approximate city-level location, network provider and the page you wrote from. We use them to reply with context and to tell a real message from an automated one. Delivery goes through Cloudflare. None of this is used for marketing, shared with third parties or turned into a profile: it travels in that email and stays there. The support form also sends which product you're writing about, so your message reaches the right place. ## Website & cookies This website uses Google Analytics 4 to measure traffic. By default it runs in cookieless mode (Google Consent Mode): analytics cookies are only set if you accept them in the cookie banner, and you can reject them — the site works the same. Your theme (light/dark) preference is also stored locally in your browser. ## Contact For privacy questions, email support@mboxviewerpro.com or reach Color Vivo Internet, S.L. --- Last updated: August 2026 # Refunds Mbox Viewer is sold through the Mac App Store and, on Windows, through the Microsoft Store. Because the app store is the seller of record, refunds are requested from and granted by the store — not by us directly. Here's how to do it in each one. This policy covers Mbox Viewer only. Takeout Reports is free, has no purchases and therefore nothing to refund. ## Mac App Store purchases Apple handles all payments and refunds for the Mac App Store. To request a refund, go to reportaproblem.apple.com and sign in with your Apple Account, find the Mbox Viewer purchase, choose “Report a Problem” or “Request a refund”, pick a reason and submit. You can also use the “Report a Problem” link in the receipt email Apple sent you. Apple reviews and decides each request according to its own refund policy. Approved refunds are returned to your original payment method. ## Why we can't refund you directly For App Store purchases, Apple is the merchant of record: it processes the payment and we never receive your card details. Developers have no way to issue refunds for App Store purchases, so every refund must go through Apple. The Microsoft Store works exactly the same way: there, the seller is Microsoft. ## Try before you buy Mbox Viewer is free for files up to 1 GB, with every feature included. We recommend opening a few of your archives in the free version before unlocking unlimited size, so you can confirm it works for you first. ## Microsoft Store purchases The Windows version is sold on the Microsoft Store, so Microsoft handles the payments and the refunds. To request one, open your Microsoft account order history (account.microsoft.com/billing/orders), find the Mbox Viewer purchase, choose “Request a refund”, give a reason and submit it. You can follow it in the refund status tab of that same order history. Microsoft is stricter about this than Apple, and it's worth knowing before you buy: its policy states that digital goods — apps included — are not refundable unless the offer or applicable law entitles you to a refund, as EU consumer law does. Microsoft reviews every request; processing can take up to 72 hours, and an approved refund goes back to your original payment method in about 3–5 business days. Online returns aren't available in every market. ## Need help? If you run into trouble requesting a refund, or you bought the wrong thing, contact us at support@mboxviewerpro.com and we'll point you in the right direction. --- # How can we help? Check the FAQ and guides, or write to us directly. We usually reply within 1–2 business days. ## Before you write - [Frequently asked questions](https://mboxviewerpro.com/faq/) - [Step-by-step guides](https://mboxviewerpro.com/guides/) - [Changelog & releases](https://mboxviewerpro.com/changelog/) [support@mboxviewerpro.com](mailto:support@mboxviewerpro.com) ## Send us a message --- ![](https://mboxviewerpro.com/_astro/appicon.DZ-pr8RP_1oCELY.webp) Another app from the makers of Mbox Viewer # Takeout Reports See what's inside your Takeout You ask Google for your archive, it takes days to arrive, and then ten ZIP files of twenty gigabytes each land on your computer. Now what? Takeout Reports opens them and tells you what's inside — without unzipping a thing. `Free` `macOS 14+` `Windows 10/11` `18 languages` `No network access` [Get it on the Mac App Store](https://apps.apple.com/app/takeout-reports/id6805066686) [Get it on the Microsoft Store](https://apps.microsoft.com/store/detail/9P4ZDR3DJK03) ![Takeout Reports on macOS: the summary of an archive, with the headline figures on top and every service with data listed below, each with how many records it holds.](https://mboxviewerpro.com/_astro/report-en-light.B7pwSFv8_1vspMP.webp) ![Takeout Reports on macOS: the summary of an archive, with the headline figures on top and every service with data listed below, each with how many records it holds.](https://mboxviewerpro.com/_astro/report-en-dark.BAtRexKm_Z26HQ4G.webp) ## It reads the archive where it sits No extracting, no copying, no duplicating: it reads each file directly inside the ZIP. It doesn't matter that the archive is 200 GB and you have thirty free on disk. Multi-part volumes are presented as a single tree, and if one is missing it tells you before handing you a report with holes in it. ## It counts records, not files A service can hand you three JSON files and still be empty. The report opens what's in there and counts what you actually have: messages, senders, labels, contacts, events, photos, albums, bookmarks, sites visited, actions Google recorded about you. When it could only measure part of a service, it says so instead of pretending it measured everything. ## Offline, and you can check The app has no network access permission — not in its entitlements on macOS, not among the capabilities it declares on Windows. This isn't a promise buried in a legal page: the system wouldn't grant it even if the app asked. Your archive never leaves your computer, nothing is uploaded, and everything works the same with Wi-Fi off. No analytics either, no identifiers, no account to create. ## What you'll find The report covers every service your archive brings, and explains the ones Google declared but sent back empty. ### Mail and Groups Messages, distinct senders, Gmail labels, years covered and how many carry an attachment. ### Google Photos Photos and videos counted separately, albums, year folders, edited copies, tagged people, and how many photos ended up with no date or no coordinates. ### My Activity How many actions Google kept, which product most of them came from, and how far back they go. ### And the rest Drive, Chrome, Contacts, Calendar, YouTube, Tasks, Maps and whatever else your archive brings. ## Browse the whole archive, read-only Beyond the figures, you can walk the archive service by service and open any file to see what it holds — a photo's metadata JSON, a calendar entry, an activity log. It is read from inside the ZIP, so nothing is written to disk. ![The Takeout Reports explorer: the list of files of a service and, on the right, the contents of a photo's metadata JSON read straight from the archive.](https://mboxviewerpro.com/_astro/explorer-en-light.CDgbxFdZ_ZskAW4.webp) ![The Takeout Reports explorer: the list of files of a service and, on the right, the contents of a photo's metadata JSON read straight from the archive.](https://mboxviewerpro.com/_astro/explorer-en-dark.7nbo3vyG_Zebn9U.webp) ## Free, and staying that way The full report and browsing are free forever, with no size limit and no cap on services. Looking at what you have is not something we charge for. Coming later Paid features will come later for getting data out and transforming it: batch export, repairing photo metadata, and searching the whole archive. None of that is in this version. ## Requirements - macOS 14 or later, Apple Silicon and Intel. - Windows 10 and 11, and Windows Server. - Reads ZIP archives (recommended) and TGZ, plus the already-extracted folder. - Available in eighteen languages, on both platforms. [Get it on the Mac App Store](https://apps.apple.com/app/takeout-reports/id6805066686) [Get it on the Microsoft Store](https://apps.microsoft.com/store/detail/9P4ZDR3DJK03) ![](https://mboxviewerpro.com/_astro/logo.DLJ_eWcW_ZJp7KQ.webp) The other app · Mbox Viewer ## Found mail? That part is Mbox Viewer's When the Takeout Reports report finds mail in your archive it doesn't just count it: it says 8,763 messages and offers to open them. Reading that mailbox is the job of Mbox Viewer, our other app — the same MBOX file, on Mac and on Windows. That's why the two live in the same place. [Mbox Viewer on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Mbox Viewer on the Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) [See what Mbox Viewer does](https://mboxviewerpro.com/features/) Takeout Reports is not affiliated with or endorsed by Google. Google and Google Takeout are trademarks of Google LLC. --- Last updated: August 2026 # Terms of Service These terms govern the use of the Mbox Viewer and Takeout Reports apps and this website, owned by Color Vivo Internet, S.L. By using either app you accept these terms. ## License Mbox Viewer is distributed through the Mac App Store and the Microsoft Store, and is also subject to Apple's and Microsoft's respective terms. The free version opens files up to 1 GB; upgrading to Pro removes that limit via a one-time in-app purchase. Takeout Reports is distributed through the Mac App Store and the Microsoft Store as well, is free of charge and currently has no in-app purchases. ## Acceptable use The App is a read-only tool for viewing your own email archives. You agree to use it lawfully and not to access data you have no right to. ## Purchases and refunds All purchases are processed through the Mac App Store or the Microsoft Store. Refund requests are handled directly by Apple or Microsoft under their respective policies, as we do not process payments. This applies to Mbox Viewer only: Takeout Reports is free, so there is nothing to refund. ## Warranty Both apps are provided “as is”, without warranties of any kind: we do not guarantee that they are error-free, that they will always be available, or that any given archive can be read in full. Although they are designed never to modify your original files, we recommend keeping backups of your data. ## Limitation of liability To the extent permitted by law, Color Vivo Internet, S.L. is not liable for indirect damages or data loss arising from use of either app. ## Contact For any questions, email support@mboxviewerpro.com. --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `macos` `windows` # Nothing Happens When You Double-Click an MBOX File Double-clicking a .mbox file does nothing on Windows, and on a Mac it hands the file to Apple Mail, which tries to import it. Here is why neither system knows what to do with your mailbox, and how to fix it in a minute. [David Carrero](https://mboxviewerpro.com/author/) · September 3, 2026 Nothing happens because neither macOS nor Windows ships with any application registered for the `.mbox` extension. There is no handler, so the double-click has nowhere to go. On a Mac it may get handed to Apple Mail, which does something worse than nothing: it tries to *import* the file instead of opening it. Install a reader that registers the extension and the double-click starts working. But the reason it doesn’t is worth two minutes, because it explains several other things that look like bugs. ## Why doesn’t my computer know what this is? Because file extensions are not magic — they are a lookup table. When you double-click, the system asks “which app claimed `.mbox`?” and acts on the answer. Out of the box, nothing has claimed it, on either system. The mail apps you already have don’t claim it either, and that is deliberate on their part. Apple Mail, Outlook and Thunderbird are not readers of mail files; they are mail *clients*, built around an account and a database of their own. A loose mailbox on your desktop is not something they have a natural place for. So on Windows you get “How do you want to open this file?” and a list of programs that will all disappoint you. On a Mac you get nothing, or the beach ball, or Apple Mail deciding to help. ## Why is Apple Mail importing my file? Because importing is the only thing it knows how to do with one. And importing is not opening: - It copies every message into Mail’s own storage, so you now have two copies of a mailbox that might be 40 GB. - It can take hours, with no meaningful progress and no way to stop cleanly. - The result lands in Mail’s sidebar, mixed in with your live accounts, which is rarely where you wanted your 2007 archive to be. If you want to browse an old export and put it away again, that is the wrong tool. Nothing is damaged — the original file is still there — but you may want to delete the imported copy afterwards to get the disk space back. ## What about the .mbox that is actually a folder? If your file came from Apple Mail, you may find that `.mbox` is a *folder*, not a file. Inside it there is a file literally named `mbox`, with no extension at all, and that file is standard MBOX. The folder is Apple’s packaging. This is a common source of “my MBOX file won’t open”: people go looking inside and try to open the wrong thing, or they try to open the folder in a reader that only accepts files. [Mbox Viewer](https://mboxviewerpro.com/features/) resolves the package on its own — you point it at `Inbox.mbox` and it opens what is inside, naming the mailbox after the folder. ## And if the file is huge? Then you may be looking at a different failure that feels identical: you double-click, something starts, and then it hangs or quits. That is not the extension problem — it is a reader loading the entire file into memory before it shows you anything. With a mailbox of a few gigabytes, that is the end of the story on most machines. The fix is a reader that streams. Mbox Viewer parses the file incrementally and builds a [binary index](https://mboxviewerpro.com/glossary/binary-index/), so a 50 GB archive of around half a million messages opens in under five minutes, stays below 600 MB of RAM, and re-opens in under a second every time after that. ## Fixing the double-click Install [Mbox Viewer](https://mboxviewerpro.com/features/) — [Mac](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/), [Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/) — and it registers `.mbox`, along with `.mbx` and `.mbs` from [Eudora](https://mboxviewerpro.com/glossary/mbx/). From then on a double-click opens the mailbox for reading: no import, no second copy, and nothing written to the file you opened. If some other app has already claimed the extension and you want to change it back: - **macOS:** select the file, `⌘I`, *Open with*, choose the app, then *Change All…* - **Windows:** right-click, *Open with* → *Choose another app*, tick *Always use this app*. You can also skip the extension question entirely and drag the file onto the app’s window, which works regardless of what is registered. ## The part that matters A file that won’t open is not a damaged file. In almost every case the mailbox is fine — it is a text file, and it has been sitting there intact the whole time. What is missing is something on your computer that knows what to do with it. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `eml` `formats` # MBOX, EML, PST, OLM: Email Archive Formats Explained What's actually inside an email archive? A plain-language tour of the four formats you'll meet — MBOX, EML, PST and OLM — and how to read each one on a Mac. [David Carrero](https://mboxviewerpro.com/author/) · June 11, 2026 Sooner or later everyone ends up with a mysterious email archive: a Google Takeout download, an old work backup, a file IT handed over when you left a job. The extension tells you a lot about what you can do with it. Here’s the field guide. ## MBOX — the open standard [**MBOX**](https://mboxviewerpro.com/glossary/mbox/) is the oldest and most widely supported archive format. It’s beautifully simple: every message in a mailbox, concatenated into one plain-text file, each message starting with a line that begins `From` . Because it’s open and text-based, it has become the *lingua franca* of email exports: - **Google Takeout** delivers Gmail as MBOX - **Apple Mail** and **Thunderbird** export to it - Classic clients — Eudora, Entourage, Netscape, Evolution, Claws Mail and many more — store or export mail this way **How to read it on a Mac:** open it with Mbox Viewer — any size, read-only, fully offline. Note that some sources need one small step first: Apple Mail exports a `.mbox` *folder* whose inner file named `mbox` is the actual archive, and Thunderbird’s own mailbox files carry no extension, so you copy them and add `.mbox`. ## EML — one file per message [**EML**](https://mboxviewerpro.com/glossary/eml/) is a single email as a file: headers, body and attachments, in the raw MIME format defined by the internet’s email standards. Outlook, Thunderbird and most clients can save individual messages as `.eml`, and many systems (ticketing tools, scanners, servers) produce them in bulk. **How to read it on a Mac:** Mbox Viewer opens `.eml` files directly, alongside MBOX. A folder full of EMLs is just as browsable as a single archive. ## PST — Outlook for Windows [**PST**](https://mboxviewerpro.com/glossary/pst/) is Microsoft Outlook’s personal storage format on Windows: a proprietary database holding mail, calendar, contacts and more. It’s compact and fast inside Outlook — and opaque outside of it. **How to read it on a Mac:** not directly with an mbox reader, because PST isn’t mbox. Convert it to MBOX first with a converter tool, then open the result with Mbox Viewer. ## OLM — Outlook for Mac **OLM** is the export format of Outlook for Mac — same idea as PST, different container, equally proprietary. **How to read it:** same recipe — convert to MBOX with a converter, then open the converted file. ## The cheat sheet | Format | What it is | Open on a Mac | | --- | --- | --- | | MBOX | Whole mailbox, open standard | Mbox Viewer, directly | | EML | One message per file, MIME | Mbox Viewer, directly | | PST | Outlook (Windows) database | Convert to MBOX first | | OLM | Outlook for Mac export | Convert to MBOX first | If you get to choose your export format, choose MBOX: it’s open, future-proof, and twenty years from now it will still be plain text you can read with whatever tools exist then. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `formats` `mbox` `pst` `history` # A Field Guide to Email Storage Formats: History, Anatomy and a Comparison How email is actually stored on disk — MBOX, Maildir, EML, PST, OST, OLM, MSG, NSF and historical formats like Eudora. Their history, how they're built, what each one is good for, and a side-by-side comparison. [David Carrero](https://mboxviewerpro.com/author/) · June 18, 2026 Every email program has to answer the same question: *where do the messages actually go on disk?* Half a century of answers has produced a small zoo of formats — some open and beautifully simple, others proprietary databases you can’t read without the app that made them. This is a tour of the ones you’ll meet, how they’re built, where they came from, and how they stack up. Broadly, they fall into three families: 1. **Open, text-based containers** — one file holds many messages (MBOX), or one file per message in a folder (Maildir). Human-readable, vendor-neutral. 2. **One message per file** — a single message as a standalone file (EML, MSG). 3. **Proprietary databases** — a binary store holding mail plus calendar, contacts and state (PST, OST, OLM, NSF). Compact inside their app, opaque outside it. ## The open, text-based formats ### MBOX — the lingua franca [**MBOX**](https://mboxviewerpro.com/glossary/mbox/) dates back to the early Unix mail systems of the 1970s. The idea is disarmingly simple: concatenate *every* message in a mailbox into one plain-text file, and mark where each one starts with a line beginning `From` (the “From\_ line”, with a space, not the `From:` header). Headers, body and [attachments](https://mboxviewerpro.com/glossary/attachment/) — encoded as text — all live inline. That simplicity hides a famous wrinkle: what happens when a message body itself contains a line starting with “From ”? Different answers gave rise to **variants** — `mboxo`, `mboxrd`, `mboxcl` and `mboxcl2` — which escape (or don’t) that sequence differently. In practice modern tools read them all. MBOX is what **Google Takeout**, **Apple Mail**, **Thunderbird** and most classic clients export, which makes it the closest thing email has to a universal archive format. ### Maildir — one file per message Created for the **qmail** server in 1995, [**Maildir**](https://mboxviewerpro.com/glossary/maildir/) takes the opposite approach: every message is its own file inside a folder, split across `tmp/`, `new/` and `cur/` subdirectories. Its great virtue is **safety without locking** — two processes can deliver mail at the same time without corrupting a shared file, the classic risk with MBOX. It’s the native format of servers like Dovecot and Courier. The trade-off is millions of tiny files, which some filesystems dislike. ### EML — a single message, the way the internet defines it [**EML**](https://mboxviewerpro.com/glossary/eml/) is one message saved exactly as it travels: the raw [MIME](https://mboxviewerpro.com/glossary/mime/) structure defined by the email RFCs (822 → 2822 → 5322). [Headers](https://mboxviewerpro.com/glossary/header/) at the top, then the body and attachments encoded in [MIME](https://mboxviewerpro.com/glossary/mime/) parts. Because it *is* the on-the-wire format, almost everything can produce and read it — Outlook, Thunderbird, ticketing systems, scanners and mail servers. A folder of `.eml` files is the simplest possible archive. ## The proprietary databases ### PST — Outlook’s personal store on Windows [**PST**](https://mboxviewerpro.com/glossary/pst/) (Personal Storage Table) is Microsoft Outlook’s on-disk database on Windows, built on the MAPI model. It holds far more than mail — calendar, contacts, tasks, notes — in one binary file. The original **ANSI** PST (Outlook 97–2002) capped out at **2 GB** and was prone to corruption near that limit; the **Unicode** PST (Outlook 2003+) raised it to **20–50 GB**. Fast and compact inside Outlook, but useless to other apps without conversion. ### OST — the offline cache **OST** (Offline Storage Table) is PST’s sibling: a *cached* copy of a mailbox that lives on an Exchange or Microsoft 365 server. It exists so Outlook works offline and re-syncs later. Crucially, an OST is tied to its account and profile — it isn’t a portable archive, and orphaned OST files can be hard to open at all. ### OLM — Outlook for Mac **OLM** is the export/archive format of Outlook for Mac. Same intent as PST, different container — a proprietary bundle that, like PST, needs converting before anything but Outlook can read it. ### MSG — a single Outlook message [**MSG**](https://mboxviewerpro.com/glossary/msg/) is one message exported from Outlook, stored as an OLE “compound file” (a mini-filesystem inside a file) carrying MAPI properties. It’s the Windows counterpart to EML, but binary and Microsoft-specific. ### NSF — Lotus Notes / HCL Domino **NSF** (Notes Storage Facility) is the database behind IBM/Lotus Notes (now HCL Domino) — an entire application platform, not just mail. NSF archives still surface in long-running enterprises and, like the others here, require dedicated tools to extract. ## The historical ones - **Eudora** (1988–2006) was the dominant client of the early internet era. It stored mail in **`.mbx`** mailbox files — essentially MBOX — paired with a **`.toc`** table-of-contents index. Because the body is MBOX-like text, Eudora archives are usually recoverable today. - **Outlook Express** used **`.dbx`** files (one per folder) on Windows through the late 1990s and 2000s; its successor **Windows Mail / Live Mail** moved to individual **`.eml`** files. - **Netscape/Mozilla** mail, **Evolution**, **Claws Mail**, **Entourage** and others stored or exported MBOX — which is exactly why MBOX remains so widely readable. ## Side-by-side | Format | Structure | Open? | Portable archive? | Origin | | --- | --- | --- | --- | --- | | MBOX | One text file, many messages | ✅ Open | ✅ Excellent | Unix, 1970s | | Maildir | One file per message, in folders | ✅ Open | ✅ Good | qmail, 1995 | | EML | One message, raw MIME | ✅ Open | ✅ Excellent | Internet RFCs | | MSG | One message, OLE compound | ❌ Proprietary | ⚠️ Limited | Microsoft | | PST | Binary database (mail + PIM) | ❌ Proprietary | ⚠️ Convert first | Outlook (Win) | | OST | Cached server mailbox | ❌ Proprietary | ❌ Account-bound | Outlook/Exchange | | OLM | Proprietary bundle | ❌ Proprietary | ⚠️ Convert first | Outlook (Mac) | | NSF | Application database | ❌ Proprietary | ⚠️ Convert first | Lotus Notes | ## What to choose for the long term For *archiving* — keeping mail readable for decades — the open, text-based formats win every time. MBOX and EML have no vendor, no licence and no database engine to go obsolete: in twenty years they’ll still be plain text any tool can open. That’s why, if you ever get to pick an export format, **MBOX** (or a folder of **EML** files) is the safe choice, and why converting PST/OLM to MBOX future-proofs an Outlook archive. Once your mail is in MBOX or EML, [Mbox Viewer](https://mboxviewerpro.com/) opens it on Mac and Windows — any size, read-only, fully offline. For the practical “which file can I open and how” version of this guide, see [MBOX, EML, PST, OLM: Email Archive Formats Explained](https://mboxviewerpro.com/blog/email-archive-formats-explained/); to turn an Outlook file into MBOX, see [how to convert PST/OLM to MBOX](https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `history` `legacy` `mbox` # Eudora: The Email Client of the Early Internet, and How to Read Its Mail Today Steve Dorner wrote it in 1988 and named it after a short story. Qualcomm sold it to eighteen million people. It died in 2006, and in 2018 the Computer History Museum published its source code under a BSD licence. If you still have a Eudora folder on an old disk, its mail is in mbox — and it opens today. [David Carrero](https://mboxviewerpro.com/author/) · August 31, 2026 There is a decent chance that somewhere in your house there is a drive with a folder called `Eudora` on it. Inside it: files named `In`, `Out`, `Trash`, each with an `.mbx` extension, each next to a `.toc` of the same name. Twenty-something years of correspondence from a time when checking mail meant dialling in on purpose. The program that wrote those files is worth remembering, and — the practical half of this post — the mail in them is not lost. It never was. ## A program named after a short story **Steve Dorner** wrote the first Eudora in 1988 at the University of Illinois at Urbana-Champaign. It took a little over a year, ran only on the Macintosh, and was about 50,000 lines of C. The name comes from Eudora Welty’s short story *Why I Live at the P.O.* Dorner’s explanation was that while writing an email program he “felt like I lived at the post office”. It is a better origin story than most software gets, and it fits: Eudora’s whole design was about the post office being *yours* — mail came down to your machine, into your files, where it stayed. That is also why this is a story with a happy ending for anyone’s archive, and we will get to that. ## The Qualcomm years Qualcomm licensed Eudora from the University of Illinois in **1991** and released it as a commercial consumer product in **1993**. Dorner joined the company and kept working from Illinois; the Windows versions were built in San Diego by Jeff Beckley and Jeff Gehlhaar. At its height the team passed fifty people, and by 2001 more than a hundred person-years had gone into the program. The numbers from that era still look odd today. By 1996 Eudora had around **18 million users**. IDC reported Qualcomm claiming **64.7% of email software revenue in 1995** — for a single client, on machines that mostly dialled a modem to fetch mail. It also went through nearly every business model there is, in order: free “postcard-ware” at the start, then a free version funded by advertising, then a paid version at $19.95 that eventually reached $65. Anyone arguing about software pricing in 2026 is having a conversation Eudora finished thirty years ago. The last releases Qualcomm shipped came out on **11 October 2006** — 7.1.0.9 for Windows and 6.2.4 for the Macintosh. Then Qualcomm sponsored a replacement built on Mozilla Thunderbird: a beta labelled 8.0 in August 2007, and a 1.0 renamed **Eudora OSE** in September 2010. It did not take. The data format was not compatible with what people already had and the experience was not the one they knew, which is a compact description of why most rewrites of beloved software fail. The project was eventually abandoned. ![Eudora 7 for Windows, its About window showing version 7.1.0.9 in Sponsored Mode and the Qualcomm copyright, 1991–2006](https://mboxviewerpro.com/_astro/eudora-mail-screenshot.ql9l3VkV_14ttEh.webp) *Eudora 7.1.0.9 — the last Windows release, running in the ad-funded Sponsored Mode — on a Windows 10 desktop, years after the program was discontinued. Screenshot from [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Eudora_mail_screenshot.jpg), credited there to Qualcomm / Computer History Museum and published under the [GPL](https://www.gnu.org/licenses/gpl.html).* ## 2018: the source code goes public In 2018, after **five years** of discussions with Qualcomm, the **Computer History Museum** published the Eudora source code under a **BSD licence** — permissive enough for personal and commercial use, with the usual requirement to keep the copyright notices, and one specific exclusion: the licence does not grant the Eudora™ trademark or the eudora.com and eudora.org domains. What was released is the real thing, not a demo: **8,651 files in 565 folders (458 MB)** for the Windows version, and **1,433 files in 47 folders (69.9 MB)** for the Macintosh one. The museum added its own copyright notice and the licence, removed third-party components it had no right to distribute, and — at Qualcomm’s request — sanitised the profanity in the comments, which tells you something honest about how commercial software actually gets written. The museum’s [account of the release](https://computerhistory.org/blog/the-eudora-email-client-source-code/) is worth reading in full, including a detail that matters here: in the first two weeks, around a thousand people answered their survey, roughly **40% of them still using Eudora**, some with archives of **300,000 messages and more**. Twelve years after the last release. Those people had a very practical reason to stay. They had decades of mail in it, and moving decades of mail is exactly the thing that goes wrong. ## The part that saves your archive: `.mbx` is mbox Eudora stored each mailbox as a plain text file with an `.mbx` extension, alongside a `.toc` table-of-contents file that served as its index. The `.toc` is Eudora’s own; you can ignore it. The `.mbx` is [mbox](https://mboxviewerpro.com/glossary/mbox/) in all but name: messages one after another, each beginning with a `From` envelope line, headers, blank line, body. Eudora’s envelope lines usually read `From ???@???` rather than a real address — it filled in a placeholder — which looks alarming and changes nothing. The real sender is in the `From:` header where it belongs, and any parser that reads the headers instead of guessing from the envelope handles it. We checked ours against a mailbox written that way: dates, senders and subjects all come out correctly. One thing genuinely is missing from the file, and it is worth knowing before you go looking: **Eudora detached attachments**. Rather than keeping them encoded inside the message, it wrote them to a separate attachments folder and left a line in the body reading `Attachment Converted: "C:\Eudora\Attach\report.pdf"`. So a Eudora mailbox will show attachments as references, not as files — unless you also kept that folder. If you are recovering an old Eudora archive, copy the whole `Eudora` directory, not just the `.mbx` files. ## Reading it today Nothing needs converting, and nothing needs Eudora. **Mbox Viewer** opens `.mbx` files directly on Mac and Windows — the extension is registered along with `.mbox` and `.mbs`, so a double-click is enough, with no renaming. **[mboxShell](https://mboxviewerpro.com/mboxshell/)**, the open-source terminal tool behind it, opens the same files from a shell on Linux, macOS, FreeBSD and Windows, and does not care about extensions at all. Either way the file is read, never written: whatever survived on that drive stays exactly as it was. If your archive is broader than Eudora — Entourage, Netscape, PowerMail, Mulberry — our guide to [reading old email archives on a modern Mac](https://mboxviewerpro.com/blog/read-old-email-archives-on-modern-mac/) covers the rest of the family, and [the history and anatomy of email formats](https://mboxviewerpro.com/blog/email-formats-history-and-anatomy/) explains why some of them survived and others took their mail with them. ## What Eudora actually left behind Ask what a dead program leaves and the answer is usually “nothing, and a folder you cannot open”. Eudora left something better: source code that anyone can read, and mail files that outlived the company, the operating system and the modem. That is not luck. It is the consequence of one decision made in 1988 — store the messages as text, one after another, in a file the user owns. Every format that chose a proprietary database instead has spent the years since generating a small industry of recovery tools. Eudora’s archives just open. Thirty-eight years is a long time for a file format to keep working. It is worth thinking about the next time you choose where your mail lives. --- *Eudora is a trademark of its respective owner. This article is not affiliated with or endorsed by Qualcomm or the Computer History Museum.* ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `gmail` `archives` # How Do You Work With an MBOX File? You asked Google for your data, waited days, and got a file you cannot open. Here is what to actually do with an MBOX file: read it, search it, pull messages out of it, and keep it somewhere it will survive. [David Carrero](https://mboxviewerpro.com/author/) · September 1, 2026 Install a reader, open the file, and read it — you do not import it, convert it, or unpack it. An MBOX file is a mailbox; the job is to open it and search it. Everything below is what that looks like in practice, and what to do afterwards. This question gets asked constantly, most often by someone who has just downloaded a Google Takeout export and found one enormous file where they expected a folder of emails. It is a fair thing to be confused about, because nothing on your computer offers to do anything useful with it. ## What am I even looking at? One file containing all your messages, one after another, in plain text. Not a database, not an archive to extract, not a folder in disguise. [We explain the format here](https://mboxviewerpro.com/blog/what-is-an-mbox-file/); the practical consequence is that the file is a *container you read*, not a package you install. Two things follow from that, and they are the two that trip people up: - **There is nothing to extract.** No unzip step, no import wizard. If a tool asks you to import your MBOX into it, it is proposing to make a second copy of your mail in its own format. Sometimes you want that. Usually you don’t. - **Size is not a problem with the file.** A 40 GB mailbox is a perfectly valid MBOX. It is a problem with whatever you try to open it in. ## Just let me read my mail Install [Mbox Viewer](https://mboxviewerpro.com/features/) on [Mac](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/) or [Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/), then drag the file onto the window. That is the whole procedure. It reads the file in place, never writes to it, and needs no account, no server and no internet connection. Mailboxes up to 1 GB open free. Bigger ones need the one-time Pro purchase, which exists because of what large files cost to support, not because the reading is different. If your file came from Gmail, your labels come with it: Takeout stores them in a header, and they show up in the sidebar with live counts, so you can browse `Receipts` or `Travel` the way you did in Gmail. ## How do I find one specific email? Search, with the same kind of syntax you already know from Gmail: `from:`, `to:`, `subject:`, `body:`, `date:`, `has:attachment`, `size:>`, exact phrases in quotes, `OR`, and negation. There is a [cheat sheet](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/) if you want the whole set. The useful trick is combining them. `from:hmrc has:attachment date:2019..2021` is the kind of query that turns an afternoon of scrolling into four results. ## How do I get messages *out* of it? This is the part most people actually need, because the mailbox is rarely the deliverable. Someone wants *these emails*, not your archive. - **One message, to send or file:** export it as [EML](https://mboxviewerpro.com/glossary/eml/), or save it as PDF or self-contained HTML. One at a time is free; doing it in batches is Pro. - **A set of messages, as a new mailbox:** narrow the archive by search, by label, or by hand, and write the selection to a brand-new MBOX file containing only those. The original is untouched. This is the delivery step of a records request or a legal hold, and it is why the feature exists. - **The data, for a spreadsheet:** export to CSV — UTF-8 with a BOM, so Excel opens it without mangling accents. - **Attachments:** save them individually or in bulk, or drag them straight to Finder or Explorer. ## What if the file is broken? It happens, especially with old backups and interrupted downloads: a mailbox where the message boundaries have been damaged, so a reader shows you three hundred messages where there were three thousand, or one absurd message that never ends. A deep scan re-detects the boundaries and writes a repaired copy to a new file. The damaged original is never modified — if the repair guesses wrong somewhere, you still have exactly what you started with. ## Where should I keep it? Wherever you keep things you would be upset to lose, in more than one place. An MBOX file is unusually good at surviving: it is text, it compresses well, and it does not depend on any particular program remaining available. A copy on an external disk and a copy somewhere off-site is enough. One thing worth doing while you still remember what it is: give it a name that will mean something in ten years. `takeout-20260901.mbox` is a filename. `gmail-personal-2004-2026.mbox` is a label your future self can read. ## And if it came from Google Takeout? Then there is probably a lot more in that download than mail — photos, activity, contacts, calendars, and services that came back empty. [Takeout Reports](https://mboxviewerpro.com/takeoutreports/), our other Mac app, opens the archive and tells you what is inside without unzipping it. It is free. --- *Google and Google Takeout are trademarks of Google LLC.* ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `archives` `product` # How to Open a 50 GB MBOX File Big MBOX files don't crash readers because they are corrupt — they crash them because most readers load the whole file into memory first. What a streaming parser and an index change, with real numbers. [David Carrero](https://mboxviewerpro.com/author/) · September 11, 2026 Use a reader that streams the file instead of loading it. With one, a 50 GB mailbox of around half a million messages opens in under five minutes, stays below 600 MB of RAM, and re-opens in under a second from then on. Without one, the size of your file is irrelevant: the reader will fall over somewhere between 500 MB and 2 GB regardless. ## Why does everything else choke? Because the straightforward way to write a mail reader is to parse the file, build a list of messages in memory, and show it. That works beautifully in testing, where the sample mailbox is 40 MB. Then someone opens a Gmail export. The parser now wants to hold half a million messages in RAM at once, the process balloons past what the machine has, and you get a spinner that never ends, a crash, or — worst of all — a window that appears after twenty minutes and stutters on every click. The file is not the problem. A 50 GB [MBOX](https://mboxviewerpro.com/glossary/mbox/) is a perfectly ordinary MBOX; the format has no size limit and never did. What has a limit is the assumption that everything fits in memory. ## What streaming actually means A [streaming parser](https://mboxviewerpro.com/glossary/streaming-parser/) walks the file in small pieces — Mbox Viewer uses a 1 MB buffer — and records *where* each message starts instead of keeping the message itself. Memory use depends on how many messages there are, not on how big they are, and a cache holds the handful you are actually reading. The practical consequence: opening a 50 GB archive costs about as much RAM as opening a 500 MB one. The numbers we publish, from the [features page](https://mboxviewerpro.com/features/): | Size | Messages | First open | Re-open | RAM | | --- | --- | --- | --- | --- | | 500 MB | ~5,000 | < 5 sec | < 1 sec | < 100 MB | | 5 GB | ~50,000 | < 30 sec | < 1 sec | < 200 MB | | 50 GB | ~500,000 | < 5 min | < 1 sec | < 600 MB | ## Why the second open is instant Because that first pass produces something worth keeping: a [binary index](https://mboxviewerpro.com/glossary/binary-index/) of where every message begins. Re-opening means loading the index, not re-reading 50 GB. The index is validated with SHA-256, so if the mailbox changes underneath it — you replaced the file, or appended to it — the app notices and rebuilds instead of showing you a stale list. It lives outside your mailbox, which stays byte-for-byte as it was. Five minutes once, a second every time after that. For an archive you consult occasionally over years, that ratio is the whole difference between a file you use and a file you avoid. ## Does search still work at that size? Yes, and it is the reason to bother. Half a million messages is not something you scroll; it is something you query. `from:`, `to:`, `subject:`, `body:`, `date:`, `has:attachment`, `size:>`, exact phrases, `OR` and negation — the [cheat sheet](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/) has the full set. Body search does read through the mail, so on a very large archive it is measured in seconds rather than instantly. Header searches — sender, subject, date — come back immediately, and they answer most questions. ## Should you split the file instead? Sometimes, but less often than people assume. Splitting is worth it when you actually need the pieces separately — one file per year to archive, or a slice to hand to someone. It is not worth it merely to make the file openable, because it does not fix anything if your reader’s problem is the reader. If you do want to split, we have [a guide for large Thunderbird mailboxes](https://mboxviewerpro.com/blog/how-to-split-large-thunderbird-mbox-files/). And if what you need is to hand over a subset, exporting a selection as a new MBOX is cleaner: search or filter down to what is in scope, write those messages to a new file, and leave the original alone. ## Practical notes for very large archives - **Disk space:** you need room for the index, not for a copy of the mail. It is a fraction of the mailbox. - **Do not put it on a network share** for the first open. Streaming means reading the whole file once, and doing that over Wi-Fi turns five minutes into an afternoon. Copy it locally, open it, put it back. - **Multi-part Takeout exports:** Google splits very large mailboxes into several files. Each one opens on its own, and they can be merged into a single mailbox, with duplicate messages removed by [Message-ID](https://mboxviewerpro.com/glossary/message-id/) if the parts overlap. - **The free version opens up to 1 GB.** Above that it is a one-time purchase — no subscription, no account. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `thunderbird` `mbox` `archives` # How to Split Large Thunderbird Mailbox Files Without Losing Emails A Thunderbird folder is a single mbox file, and after fifteen years it can weigh more than the disk it started on. Here is how to cut one into smaller mailboxes — with Mbox Viewer or with mboxShell, our open-source terminal tool — and, more importantly, how to prove afterwards that not a single message was lost. [David Carrero](https://mboxviewerpro.com/author/) · August 25, 2026 A Thunderbird folder is not a folder. It is one file, holding every message you ever received, one after another, in the order they arrived. That design has aged remarkably well — it is why a mailbox written in 2004 still opens today — but it has one consequence people discover late: after fifteen years, your Inbox is a single 14 GB object, and everything you might want to do with *part* of it involves moving *all* of it. Sooner or later there is a reason to cut it up. A lawyer asks for one year of correspondence. You are leaving a company and only the project mail is yours to take. You want the 2008–2015 half on an external drive and the rest in daily use. Or the folder has simply become unwieldy and you want it in slices you can back up separately. The advice you will find in forums is to cut the file with `split`, or with a text editor, or with `csplit` on `/^From /`. Please do not. Here is why, and here is what to do instead. ## Why cutting an mbox by hand goes wrong An [mbox](https://mboxviewerpro.com/glossary/mbox/) file is a plain concatenation: each message begins with a line starting `From` — the *envelope* line, not the `From:` header — and runs until the next one. That is the whole format. Cut that file at an arbitrary byte or line offset and you will land in the middle of a message roughly every time. The first part ends with half a set of headers; the second begins with a body that has no headers at all and is not a message any more, just text. Both files still *look* fine — they open, they are the right size — and the damage is only visible when you go looking for one specific email years later. Cutting on the `From` pattern is smarter and still not safe. The mbox family escapes a body line that begins with `From` by writing it as `>From` , but not every program that ever wrote your mailbox did so, and a quoted reply can easily contain a line that starts with “From ”. Split on the pattern and that message tears in two — one email becomes two half-emails, and nothing tells you it happened. Which is the real problem with all the by-hand routes: **they give you no count**. You do not know how many messages went in, how many came out, or whether the numbers match. The safe way to split a mailbox is to treat it as mail rather than as text — parse it, select whole messages, write them back out — and then check the arithmetic. ## Before you cut: three things about Thunderbird’s files Each mailbox lives as one extension-less file inside your profile: - **Windows:** `%APPDATA%\Thunderbird\Profiles\\Mail\Local Folders\` - **macOS:** `~/Library/Thunderbird/Profiles//Mail/Local Folders/` - **Linux:** `~/.thunderbird//Mail/Local Folders/` Inside you will find `INBOX`, `Sent`, `Archives` and your own folder names, each next to an `.msf` file of the same name. The `.msf` is Thunderbird’s index and can be ignored — it is rebuilt on demand. The extension-less file is the mail itself, in standard mbox format. (There is a fuller tour in our guides for [macOS](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-mac/) and [Windows](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-windows/).) Three rules before you touch anything: **Quit Thunderbird.** It keeps the file open and writes to it; splitting a mailbox that is being appended to is how you get a half-message at the end. **Work on a copy.** Copy the mailbox file somewhere else — the Desktop is fine — and split the copy. Never move the original out of the profile: Thunderbird will decide the folder is gone. **Compact first, or know what you are keeping.** When you delete a message, Thunderbird marks it and leaves it in the file; the bytes go away only when the folder is compacted. That is why a folder showing 4,000 messages can be 9 GB. If you split without compacting, those deleted messages come along into your pieces — they are still perfectly readable mail. Right-click the folder → **Compact** first if you do not want them, and skip it deliberately if you do. ## Step 1 — measure before you cut Before deciding where the cuts go, look at what is actually in the file. [mboxShell](https://mboxviewerpro.com/mboxshell/), our open-source (MIT) terminal tool, reads Thunderbird’s extension-less files directly, has no size limit, and never writes to the file it opens: ``` $ mboxshell stats INBOX File INBOX File size 9.41 GiB Messages 128,455 Date range 2004-02-11 — 2026-08-19 Index size 14.2 MiB Indexing time 48.31s With attachments 19,880 (15.5%) Duplicates 312 (128,143 Unique IDs) ``` Write those two numbers down — **message count** and **date range**. They are what you will check against at the end. Now plan the cuts without producing anything. `search` counts a slice for you, so you can try boundaries until the pieces are the size you want: ``` $ mboxshell search INBOX "after:2004-01-01 before:2010-01-01" --json | head -3 { "result_count": 31204, ``` `after:` includes its own day and `before:` excludes it, so consecutive ranges written this way meet exactly — no gaps, no overlaps. That property is what makes the final check work. The [full search syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/) also lets you slice by sender, by size or by attachment instead of by date, if that is what your split is really about. ## Step 2 — cut the mailbox **With Mbox Viewer**, on [Mac or Windows](https://mboxviewerpro.com/features/), the split is the export you already know: 1. Open the copied mailbox file — the extension-less one, no renaming needed. 2. Search for the slice: `after:2004-01-01 before:2010-01-01`. 3. Select the messages: click the first row, then Shift-click the last one to take the whole range. 4. **File → Export** (⌘E) → **MBOX**. On Windows it is **Export → To MBOX…**, and there you can skip step 3 entirely: with nothing selected it exports everything the search left on screen. You get one new mailbox file, offered as `INBOX-selection.mbox`, holding exactly those messages. They are copied byte for byte, so the result is a valid mailbox that any client opens, and the file you opened is never touched — the app is strictly read-only. Repeat for each slice. Exporting to MBOX is part of the free tier; what the free tier limits is the size of the mailbox you open, which is 1 GB. **With mboxShell only**, the route is now direct. Since v0.7.2, `export --format mbox` writes the selection straight back out as a mailbox, so each slice leaves in the same format it arrived in: ``` $ mboxshell export INBOX --format mbox --query "after:2004-01-01 before:2010-01-01" --output ./2004-2009.mbox Exported MBOX mailbox to ./2004-2009.mbox (31204 message(s)) ``` Messages are copied byte for byte and the file you read is never touched; the output goes to a temporary file that is renamed at the end, so an interrupted run never leaves a half-written mailbox under the name you asked for. It is free, it has no size limit, and it scripts. Before v0.7.2 the terminal-only route was to export each slice as a folder of [EML](https://mboxviewerpro.com/glossary/eml/) files and let Thunderbird rebuild the mailbox on import — `--format eml` still does exactly that. The other half of the job, putting mailboxes *together*, is `mboxshell merge a.mbox b.mbox -o merged.mbox`. ## Step 3 — prove that nothing was lost This is the step that separates a split from a gamble, and almost nobody does it. **Count each piece.** Run `stats` on every slice and add up the message counts. The total has to equal what the original reported. If it is short, a boundary is wrong; if it is over, two slices overlap. **Check the date ranges.** Each piece’s range should sit inside the boundary you asked for, and the pieces should line up end to end with no hole between them. **Rebuild the original and compare.** This is the decisive one. Merge the pieces back together — deduplication by [Message-ID](https://mboxviewerpro.com/glossary/deduplication/) is on by default — and read the summary: ``` $ mboxshell merge 2004-2009.mbox 2010-2017.mbox 2018-2026.mbox -o rebuilt.mbox Merge complete: Input files 3 Total messages 128,455 Duplicates removed 0 Output size 9.41 GiB Output file rebuilt.mbox ``` `Total messages` matching the original count and `Duplicates removed` at zero together say that your slices were complete *and* disjoint: every message is in exactly one of them. If duplicates appear, your ranges overlap. If the total is low, something fell between two cuts. Either way you know before you delete anything — which is the whole point. Only now is it reasonable to archive the original away. And even then: keep it. Disks are cheaper than the email you cannot get back. ## Step 4 — put the pieces back into Thunderbird If the slices are meant to stay in Thunderbird as separate folders, the free [ImportExportTools NG](https://addons.thunderbird.net/thunderbird/addon/importexporttools-ng/) add-on imports an mbox file straight into Local Folders as a new folder — and can also import a directory of EML files, which is what closes the mboxShell route. Do it with Thunderbird running, through the add-on, rather than by dropping files into the profile by hand; that way Thunderbird builds its own `.msf` index and knows what it has. And if the pieces are not meant to go back — the year that goes to the lawyer, the archive that goes on the external drive — they do not need to. They are standard mbox files. Mbox Viewer opens them, mboxShell opens them, and so will whatever reads mail in twenty years, which is more than can be said for most of the formats that came after. ## What not to do - **Do not delete the original** until the arithmetic in Step 3 checks out. - **Do not split by bytes or lines** with `split`, `dd` or a text editor, and do not open a multi-gigabyte mailbox in an editor at all. - **Do not rename or move the original inside the profile.** Thunderbird tracks folders by file name. - **Do not trust a piece you have not counted.** A file that opens is not the same as a file that is complete. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `announcement` `product` `macos` # Introducing Mbox Viewer: Open Any MBOX or EML File, Instantly Why we built Mbox Viewer — a native macOS app that opens MBOX and EML files of any size with streaming performance, total privacy, and no Electron or Java in sight. [David Carrero](https://mboxviewerpro.com/author/) · May 20, 2026 Today we’re introducing **Mbox Viewer**, a native macOS app for opening, searching, and exporting MBOX and EML email archives of *any* size. If you’ve ever exported your Gmail with Google Takeout and then stared at a 12 GB `.mbox` file wondering how on earth to read it, this app is for you. ## The problem we kept running into MBOX is everywhere. It’s what Google Takeout hands you, what Thunderbird and Apple Mail export, and what shows up during migrations and e-discovery. It’s an open, future-proof format — which is exactly why it’s so valuable as an archive. The trouble is **opening** it. On a Mac, your options have always been bad: - **Apple Mail** can import MBOX, but it copies every message into your live mailbox. For a large archive that means hours of waiting and a cluttered inbox. - **Thunderbird** works, but it’s a heavyweight install just to read one file — and it buckles on multi-gigabyte archives. - **Online converters** ask you to upload your private email to someone else’s server. Hard no. - **Text editors** show you raw headers and encoded gibberish, and choke on big files. None of these respect the two things that matter most with email: **your time** and **your privacy**. ## What makes Mbox Viewer different We built Mbox Viewer from the ground up to fix this, with four principles. ### 1\. Truly native Mbox Viewer is a real macOS app — a Universal Binary that runs natively on Apple silicon. There’s **no Electron** bundling an entire web browser, and **no Java runtime** to install and babysit. It launches instantly, feels like a Mac app, and sips resources. ### 2\. Streaming, not loading Instead of pulling a whole file into memory, Mbox Viewer **streams** it. It indexes the archive and reads only the messages you actually open. The result is that a 20 GB file shows its message list almost immediately and your Mac stays responsive the entire time. There’s no arbitrary size cap. ### 3\. Privacy by default Your email **never leaves your Mac**. There’s no account to create, no cloud sync, and no telephone-home. Mbox Viewer opens your archive read-only and works completely offline. What you read stays between you and your computer. ### 4\. Built to do real work Opening a file is just the start. Mbox Viewer lets you: - **Search** across the whole archive with operators like `from:`, `subject:`, `date:`, and `has:attachment`. - **Read** messages with formatting, inline images, and full headers intact. - **Export** to EML, PDF, CSV, or plain text. - **Extract attachments** in bulk to a folder. ## Free and Pro Mbox Viewer is **free** to open and read archives up to 1 GB — plenty to try it on a real file. **Pro** unlocks unlimited file sizes and the full export toolkit, as a single one-time purchase on the Mac App Store. No subscription, ever. ## Where it came from Mbox Viewer grew out of [mboxshell](https://github.com/dcarrero/mboxshell), an open-source command-line tool for parsing MBOX files. The native app brings that same robust parsing engine to a fast, friendly macOS interface. ## Try it on your own archive Export your Gmail with Google Takeout, then open the file and see how fast “instant” really is. [Get Mbox Viewer on the Mac App Store →](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `privacy` `archives` # Is It Safe to Open an MBOX File? An MBOX file is plain text and cannot execute anything by itself. The real risks are elsewhere: attachments you save and open, remote images that report back to the sender, and readers that upload your archive to a server. [David Carrero](https://mboxviewerpro.com/author/) · September 9, 2026 Yes. An [MBOX file](https://mboxviewerpro.com/blog/what-is-an-mbox-file/) is plain text and cannot run anything by itself; opening one is as dangerous as opening a text document, which is to say not at all. The risks are in what the file *contains* and in what your reader *does* — three specific things, all of them manageable. ## Risk one: the attachments The file itself is inert, but a message inside it can carry an attachment that is not. A macro-laden spreadsheet from 2012 is exactly as harmful today as it was then, and an old archive is precisely where those live. Nothing happens while it sits in the mailbox. [Attachments](https://mboxviewerpro.com/glossary/attachment/) are stored as [base64](https://mboxviewerpro.com/glossary/base64/) text — a photo, an invoice and a piece of malware are all just characters until something decodes and runs them. The moment of risk is when you save one to disk and double-click it, and at that point the ordinary rules apply: check what it is, be suspicious of executables and macros, let your antivirus see it. Reading the message is safe. Acting on what is inside it is where judgement comes in. ## Risk two: the remote images This one is subtler and affects far more people, because it costs you nothing to fall for it. Many HTML emails do not embed their images; they link to them. Open the message and your computer fetches those files from a server, and that request tells the sender that this message was opened, roughly when, and from roughly where. On an archive it is worse than on live mail: open a mailbox from 2015 and you can quietly announce to a few hundred senders that an address they had written off is alive and reading. The answer is not to avoid opening your mail. It is a reader that does not fetch anything unless you ask. Mbox Viewer blocks remote images and sanitizes HTML by default; nothing loads from the internet until you decide it should, on a message you have looked at and want to see properly. ## Risk three: the reader itself Here is the one nobody mentions, and it is the biggest. Search for a way to open an MBOX file and a good share of the results are websites: upload your mailbox, we will show it to you in the browser. Read that offer again with the contents in mind. A Gmail export is every message you have received in twenty years — your bank, your doctor, your lawyer, password resets, the lot. Uploading it to an unknown server to *look at it* is not a reasonable trade, and if the archive is covered by a records request, a legal hold or any data-protection duty, it is not a trade you are permitted to make at all. Desktop apps deserve the same question, just asked differently: does it phone home, does it need an account, what does it do with a crash report. Mbox Viewer’s answer is that everything runs locally. No cloud, no telemetry, no account, no licence server. Pull the network cable and it behaves identically — which is the only version of this claim you can actually test, and we would rather you did. ## And is *your* file at risk from being opened? Different question, and a fair one: can opening the archive damage it? Not here. The app is strictly read-only — it never writes to the mailbox you opened. Even the repair feature, which reconstructs damaged message boundaries, writes a repaired *copy* to a new file and leaves the original exactly as it found it. The same goes for exporting a selection as a new MBOX: new file out, original untouched. That is worth checking in whatever tool you use, because “open” means different things. An import copies your mail into somebody else’s database. That is not what happens when a reader opens a file. ## The short version The file is safe. Be careful with attachments you save, use a reader that blocks remote images, and do not upload twenty years of your correspondence to a website to avoid installing an app. --- More on what the app does and does not do with your data on the [features page](https://mboxviewerpro.com/features/) and in the [privacy policy](https://mboxviewerpro.com/privacy/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `formats` `pst` # MBOX Converter: When You Actually Need One Most people searching for an MBOX converter want to read their mail, not convert it — and converting makes a second copy of an archive they already have. Here is when conversion is genuinely the answer, and what to convert to. [David Carrero](https://mboxviewerpro.com/author/) · September 5, 2026 You need a converter when another program has to receive your mail and cannot read MBOX — moving an archive into Outlook, say. You do not need one to read, search, print or share your own messages. That distinction is worth a few minutes, because conversion is not free: it produces a second copy of everything you own. ## The question behind the search Almost everyone typing “MBOX converter” is holding a Google Takeout export and wants to see what is in it. Converting is the first idea that comes to mind, because the file won’t open and converting sounds like the thing that makes files open. But conversion does not make a file readable. It makes a *different* file, in a format some other program prefers, and you still need something to read it in. If the goal is to look at your own email, you can skip the whole step: a [reader](https://mboxviewerpro.com/features/) opens the mailbox where it sits, leaves it untouched, and gets you to the same place without a second 40 GB copy on your disk. Three good reasons to convert anyway: 1. **Another program is the destination.** Someone needs the mail *in Outlook*, or in a system that ingests one specific format. 2. **You need individual messages, not a mailbox.** A handful of emails to attach to a ticket, a claim, or a filing. 3. **You need the data, not the mail.** Dates, senders and subjects in a spreadsheet, for an audit or a count. Cases 2 and 3 are not really conversion; they are *export*, and any decent reader does them without transforming your archive at all. ## What can you turn an MBOX into? | Target | What it’s for | Do you need a converter? | | --- | --- | --- | | [EML](https://mboxviewerpro.com/glossary/eml/) | One file per message, opens anywhere, easy to attach | No — export from a reader | | PDF | Filing, printing, sending something that will look the same in ten years | No — export or print | | HTML | A self-contained copy with images embedded | No — export | | CSV | Dates, senders, subjects in a spreadsheet | No — export | | A smaller MBOX | Handing over just the messages in scope | No — export a selection | | [PST](https://mboxviewerpro.com/glossary/pst/) | Getting the archive into Outlook | **Yes** — a real conversion | | [Maildir](https://mboxviewerpro.com/glossary/maildir/) | Feeding a mail server or a different client | **Yes** | Everything in the “no” half of that table, Mbox Viewer does directly: EML, PDF, HTML, CSV, plain text, attachments in bulk, and a [new MBOX file](https://mboxviewerpro.com/glossary/mbox/) containing only the messages you picked. One message at a time is free; batches are Pro. ## Going the other way: PST and OLM The conversion people genuinely need most often is the opposite of what they searched for: they have an Outlook archive — a `.pst` on Windows, a `.olm` from Outlook for Mac — and they want it *in* MBOX, where it can be read without Outlook. That one is a real conversion and needs a real tool. We keep a [step-by-step guide for PST and OLM](https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/), because it is the one route we get asked about constantly and the one where the wrong tool can quietly lose your attachments. ## What conversion costs you Worth knowing before you start, whichever direction you go: - **A second copy of everything.** Two archives to store, back up and keep track of, and two answers when someone asks what you have. - **Things that don’t survive the trip.** [Gmail labels](https://mboxviewerpro.com/glossary/gmail-labels/) are a header in an MBOX file, and most target formats have nowhere to put them. Threading gets rebuilt from headers, sometimes differently. Timestamps can shift with time zones. - **A tool you have to trust with all of it.** Many converters are web services: you upload every email you have ever received to a stranger’s server to change a file extension. For a personal archive that is a poor trade; for anything covered by a records request or a legal hold, it is not a trade you are allowed to make. Whatever you use, keep the original. A conversion you can repeat is an inconvenience; a conversion you cannot is a data loss you haven’t noticed yet. ## The rule of thumb Convert when a *destination* demands it. Export when a *person* asks for something. Read when you just want to see your mail — that one needs neither. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `education` `product` `macos` # MBOX archives for schools and organizations: the edition you buy in Apple School Manager Apple School Manager buys apps, not in-app purchases. That is why Mbox Viewer Pro for Education exists: a Custom App that arrives unlocked, bought by the seat and deployed by MDM. [David Carrero](https://mboxviewerpro.com/author/) · August 26, 2026 Every so often a message arrives from an IT department, and it is always a version of the same question: *we need Mbox Viewer on forty Macs — how do we buy forty licences?* For a while the honest answer was an awkward one. You couldn’t. Not properly, anyway. ## What Apple School Manager can and cannot buy Apple School Manager and Apple Business Manager are good at buying apps. You pick an app, you buy however many copies you need, you assign them to people or to devices through your MDM, and when someone leaves you take the licence back and give it to the next person. What neither of them buys is an **in-app purchase**. And in the Mac App Store, that is exactly how Mbox Viewer Pro unlocks: the app is free to open a mailbox, and a one-time purchase inside it removes the size limit. So the licence a school actually needed was the one thing the school could not buy. The workaround — asking forty people to each make a personal purchase and then send the receipt to accounting — is not a workaround, it is a small administrative disaster. In a district where everyone signs in with a Managed Apple ID, most of those people cannot buy anything at all. ## A Custom App is Apple’s answer to precisely this Apple has a mechanism for the case where an organization needs a build that isn’t quite the public one: the **Custom App**. It is a separate, private version of the app, distributed only to the organizations you name, with no listing in the App Store that anyone can stumble onto. **Mbox Viewer Pro for Education** is that build. Same app, same code, same read-only behaviour — with every Pro feature already unlocked, permanently, and no in-app purchase anywhere in it. It is bought by the seat inside Apple School Manager or Apple Business Manager and pushed out by MDM like any other app: Jamf, Intune, Mosyle, Kandji, Addigy, whatever you already run. The name says Education because that is the store’s category, but Apple Business Manager works the same way. A law firm and a city council buy it through exactly the same door as a university. ## What the person in front of the Mac sees Nothing. That is the whole point. They open the app and it works. There is no purchase screen to explain in a manual, no licence key to distribute over email, no account to sign into, no size ceiling to run into halfway through a job, and nothing that expires next year. IT support never gets the ticket, because there is no step where the ticket comes from. ## What organizations use it for We don’t publish who uses it. That is deliberate, and it will stay that way: a Custom App is private, and the list of organizations it goes to is theirs to talk about, not ours. What we can say is what the work looks like, because it repeats: - **Records requests and legal holds.** A Google Vault or Google Takeout export arrives, someone has to review it, narrow it down to the messages the request actually covers, and hand over those and nothing else. Since 2.8.4 the app exports a selection as a brand-new MBOX file — the original archive is never modified, and everything you excluded is simply not in the new file. - **Mailboxes of people who have left.** A former employee’s or student’s account is gone, the exported mailbox is all that remains, and someone still has to open it. - **Historical archives.** Backups and mail-server copies from a decade ago that no current client will touch. One more thing that tends to settle the decision in a school: the app has no server, no analytics and no cloud. It works with the network off. Nothing about the mail being read leaves the Mac. ## The price **39.99 USD per seat**, paid once. That is below the 44.99 USD lifetime licence in the App Store — bought in volume, each seat costs less than it does retail, which is the way round it should be. That figure is the United States price. Apple converts every other territory from it automatically, so an organization in the euro area sees 44.99 €, and a Canadian one its own equivalent. The amount that counts is the one Apple School or Business Manager shows you. No subscription, no renewal, no expiry date. Buy more seats whenever you need them, without writing to us again. ## Why there is no buy button Because there is nothing to press yet. A Custom App only becomes visible to an organization after its **Organization ID** has been added to the app’s record — until then it isn’t hidden from you so much as it doesn’t exist for you. So the first step is not a payment. It is an email telling us who you are, so your ID goes on the list. Once it is there, the app shows up in your account under *Apps and Books → Custom Apps* — Apple allows up to 24 hours for that — and you buy the seats yourself with your usual payment method. It is also why you won’t find an App Store link for this edition anywhere on our site. There is no public listing to link to, and pointing you at the regular app would be pointing you at the thing that doesn’t solve your problem. ## How to ask for it Four things get it moving: your organization’s name, its Apple School or Business Manager Organization ID (in *Settings → Enrollment Information*), roughly how many seats you need, and someone to reply to. The form and the full details are on the [Education page](https://mboxviewerpro.com/education/). If your organization runs neither Apple School Manager nor Apple Business Manager, write anyway — that is a conversation, not a dead end. And if this is for a single Mac rather than an organization, none of the above applies to you: the [regular app](https://mboxviewerpro.com/features/) is the same program, free to try, with a one-time purchase to lift the size limit. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `archives` `legacy` # Reading Old Email Archives from Eudora, Entourage and Other Classic Clients on a Modern Mac That backup from Eudora, Entourage, Netscape or PowerMail is probably standard mbox — which means a modern Mac can still read it. Here's how to find out and open it safely. [David Carrero](https://mboxviewerpro.com/author/) · June 11, 2026 Somewhere on an old drive you may have a folder from a mail program that no longer exists: **Eudora**, **Entourage**, **Netscape Mail**, **PowerMail**, **Sparrow**, **Spicebird**, **PocoMail**, **Mulberry**… The app is gone. The question is whether the mail is gone with it. Usually it isn’t. Most classic email clients stored or exported mail in the open [**mbox**](https://mboxviewerpro.com/glossary/mbox/) format — the same standard Gmail uses for Google Takeout today. If your archive is mbox, a modern Mac can open it right now, with no emulators and no resurrection of 2003-era software. ## Step 1: find the mailbox files Dig into the old mail folder and look for the largest files. Depending on the client, they may be named after mailboxes (`In`, `Out`, `Inbox`, `Sent Items`) and may have no extension, or extensions like `.mbx` or `.mbox`. Eudora, for example, kept each mailbox as a plain `.mbx` file; Netscape and Mozilla-family clients used extension-less files just like Thunderbird still does. ## Step 2: check whether it’s mbox The test takes ten seconds: open the file with any text editor (or QuickLook it) and look at the first line. A standard mbox file starts with something like: ``` From someone@example.com Mon Mar 4 09:21:33 2002 ``` If you see a `From` line followed by familiar email headers, congratulations — it’s mbox, and your mail survived. ## Step 3: add the .mbox extension and open it 1. **Copy** the file (keep the original untouched, as a backup). 2. Rename the copy to add the `.mbox` extension — `In.mbx` → `In.mbox`, `Inbox` → `Inbox.mbox`. 3. Open it with **Mbox Viewer** — drag & drop works. Mbox Viewer is strictly read-only, so even a precious one-of-a-kind archive is safe: nothing is ever written to the file. Search works across the whole archive, attachments can be previewed and extracted, and you can export anything interesting to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or text. ## When it isn’t mbox A few old clients used proprietary databases instead — Outlook Express (`.dbx`) and Outlook (`.pst`) are the usual suspects. Those need a one-time conversion to MBOX with a converter tool first; after that, the same steps apply. ## Why bother? Old mail is personal history: the apartment hunt from 2004, the first emails with someone who matters, a project that shaped your career. The mbox format’s great virtue is that it kept all of that in plain text while the apps around it came and went. Twenty minutes with an old drive and a [good reader](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/) is usually all it takes to get it back. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `mbox` `formats` `archives` # What Is an MBOX File? An MBOX file is a plain-text file holding many email messages one after another, each starting with a line that begins "From ". It is what Google Takeout hands you when you export Gmail — and what Thunderbird and Apple Mail keep your mail in. [David Carrero](https://mboxviewerpro.com/author/) · August 30, 2026 An MBOX file is a plain-text file that stores many email messages one after another, each beginning with a line that starts with `From` and a space. That is the whole format. It is what Google Takeout gives you when you export Gmail, and what Thunderbird and Apple Mail use to store mail on disk. If you have one sitting in your Downloads folder and you just want to read it, skip to [opening it on Mac](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/) or [on Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/). If you want to know what you are actually holding, read on. ## Why is it just a text file? Because it was invented in the early 1970s, when a mailbox was a file a program appended to. [MBOX](https://mboxviewerpro.com/glossary/mbox/) — short for mailbox — was never designed; it accumulated. It got a written specification only decades later, in [RFC 4155](https://www.rfc-editor.org/rfc/rfc4155), which describes it mostly to explain how to exchange one over the internet. Open one in a text editor and you can read your own email with no software at all. That is worth knowing on its own: whatever happens to the app you use today, the archive is not locked to it. Fifty years of tooling can read this format, and that is precisely why services still export to it. ## How does it know where one message ends? By a convention that sounds too fragile to have survived: a line beginning with `From` marks the start of a new message. Which raises the obvious problem — what happens when a message body contains a line that starts that way, in a quoted reply or a code sample? The answers to that question are the [variants of the format](https://mboxviewerpro.com/glossary/mboxrd/). `mboxo` puts a `>` in front of the offending line. `mboxrd` does the same but also escapes lines that already begin with `>From`, which makes the change reversible. `mboxcl` and `mboxcl2` skip the escaping and record each message’s length in a `Content-Length` header instead. You almost never need to care which one you have. It matters in exactly one situation: when a tool guesses wrong and splits a message in the middle, leaving you with a mailbox that has more messages in it than you ever received. ## What is inside a single message? Everything, encoded as text. A message has [headers](https://mboxviewerpro.com/glossary/header/) at the top — `From`, `To`, `Subject`, `Date`, plus a pile of technical ones — then a blank line, then the body. If the message has an HTML version, or a photo attached, those are [MIME](https://mboxviewerpro.com/glossary/mime/) parts inside the same message, and binary files are encoded in [base64](https://mboxviewerpro.com/glossary/base64/) so they survive as text. This is why a mailbox with a few hundred photos in it is enormous: base64 makes a file about a third larger than it was, and all of it is sitting in that one .mbox. ## Where does an MBOX file come from? Four sources cover almost everyone: - **[Google Takeout](https://mboxviewerpro.com/glossary/google-takeout/).** Export your Gmail and you get MBOX — one huge file, or several if the mailbox is very large. Gmail’s labels survive the trip, stored in a header the export writes. - **Thunderbird.** Every folder you see in Thunderbird is an MBOX file inside your profile folder, next to a `.msf` index file that only Thunderbird needs. - **Apple Mail.** Exporting a mailbox produces something confusing: a folder named `Inbox.mbox` containing a file literally called `mbox`. The folder is packaging; the file inside is standard MBOX. - **Mail servers.** Postfix, Dovecot and their relatives have stored mail this way for decades, and old backups are full of it. ## So how do you open one? Not by double-clicking, usually — neither macOS nor Windows ships with anything registered for that extension, so nothing happens, or Apple Mail tries to *import* it, which is a different thing entirely. Importing copies every message into Mail’s own storage; opening does not touch the file at all. What you want is a reader that opens the file where it sits and leaves it alone. That is what [Mbox Viewer](https://mboxviewerpro.com/features/) does on Mac and Windows: it streams through the file instead of loading it into memory, so a 50 GB archive of around half a million messages opens in under five minutes and stays below 600 MB of RAM, and it builds an index so every re-open after that takes under a second. It is strictly read-only. Mailboxes up to 1 GB open without buying anything. ## Do you need to convert it first? Almost certainly not, if what you want is to read it. Conversion only matters when some *other* program needs the mail in a different shape — a case that is rarer than the search results suggest. The conversion people genuinely need is usually the opposite one: getting an Outlook archive *into* MBOX, which has [its own guide](https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/). ## The short version It is a text file full of emails, separated by `From` lines. It is old, it is simple, and that simplicity is why your mail is still readable decades later. The awkward part was never the format — it is that operating systems don’t know what to do with it, and most readers fall over when the file gets big. --- More definitions in the [glossary](https://mboxviewerpro.com/glossary/), starting with [MBOX](https://mboxviewerpro.com/glossary/mbox/) itself. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `announcement` `product` `macos` `gmail` # What's Inside Your Google Takeout? A Free Mac App That Tells You Ten ZIP files of twenty gigabytes each, and no idea what is in them. Takeout Reports opens a Google Takeout archive and reports what it holds — how many messages, how many photos, which years, which services came back empty — without unzipping it and without touching the network. [David Carrero](https://mboxviewerpro.com/author/) · August 28, 2026 You [ask Google for your archive](https://mboxviewerpro.com/guides/how-to-export-gmail-with-google-takeout/), wait a few days, and then ten ZIP files of twenty gigabytes each land in your Downloads folder. You double-click one out of curiosity, find a folder called `Takeout` with thirty subfolders in it, and close the window. Six months later it is still there, and you still don’t know what’s in it. That is the problem **[Takeout Reports](https://mboxviewerpro.com/takeoutreports/)** solves. It is our second Mac app, it is free, and it does one thing: it opens the archive and tells you what is inside. ## A report, not a viewer There are plenty of tools that open one file out of a Takeout. This one measures the whole thing and hands you the figures: how many messages, how many photos and videos, which years they span, how many actions Google recorded about you, and which services Google declared but sent back empty. That last part matters more than it sounds. A Takeout is not a tidy backup; it is whatever Google happened to export that week. Knowing that Calendar came back with four events and Maps with none is information — about your archive, and about what Google actually kept. Version 1 gives you the figures and lets you browse the archive read-only. Opening a message, a photo or a JSON to see what it holds is included; that’s as far as it goes. ## It never unzips anything Every file is read directly inside the ZIP. No extracting, no copying, no temporary duplicate of a 200 GB archive on a disk with thirty gigabytes free. Multi-part archives — `takeout-…-001.zip`, `-002`, and so on — are presented as a single tree, and if one of them is missing you are told before you get a report with holes in it, rather than after. ## It counts records, not files A service can hand you three JSON files and still be empty. Counting files tells you nothing; the report opens what is in there and counts what you actually have — messages, senders, labels, contacts, events, albums, bookmarks, sites visited. And when it could only measure part of a service, it says so. An honest “measured in part” is worth more than a confident number that is wrong. ## It cannot reach the network — and that is checkable The app has no network access entitlement. This is not a promise in a privacy policy: it is the operating system refusing to grant something the app never asks for. Your archive does not leave your Mac, nothing is uploaded, and everything works exactly the same with Wi-Fi off. No analytics, no identifiers, no account. For an archive that contains twenty years of your mail and every photo you ever took, that seemed like the only defensible design. ## When it finds mail, Mbox Viewer takes over Takeout exports Gmail as one enormous MBOX file. Takeout Reports counts it — *8,763 messages, 330 senders, 14 labels* — and then offers to open it, because reading it is the job of the other app in the house: Mbox Viewer, on Mac and on Windows, on that very same file. That is why the two live at the same address. One tells you what you have; the other lets you read it. ## Free, and what comes next The full report and the browsing are free forever, with no size limit and no cap on services. Looking at what you have is not something we charge for. Paid features will come later, and they are all on the other side of the same line: getting data out and transforming it — batch export, repairing photo metadata, searching the whole archive. None of that is in this version, and the page doesn’t pretend otherwise. It needs macOS 14 or later, reads ZIP (recommended), TGZ and the already-extracted folder, and speaks eighteen languages. [Everything about it is here](https://mboxviewerpro.com/takeoutreports/). It has been on the Mac App Store since 27 August. [Get Takeout Reports on the Mac App Store →](https://apps.apple.com/app/takeout-reports/id6805066686) --- *Takeout Reports is not affiliated with or endorsed by Google. Google and Google Takeout are trademarks of Google LLC.* ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `announcement` `product` `macos` # What's New in Mbox Viewer 2.7.0: Faster, More Private, More Accessible Mbox Viewer 2.7.0 is a big reliability, privacy, accessibility and speed update — faster on large mailboxes, stronger tracking-pixel blocking, full VoiceOver and keyboard support, and rock-solid handling of huge or malformed files. Still strictly read-only. [David Carrero](https://mboxviewerpro.com/author/) · July 3, 2026 Mbox Viewer **2.7.0** is here — and it’s one of our biggest updates yet, even though you won’t find a pile of flashy new buttons. This release is the result of a full audit of the app, focused on the four things that matter most when you’re working through years of archived email: **reliability, privacy, accessibility and speed**. No new clutter — just a better Mbox Viewer Pro. As always, the app stays **strictly read-only** and never modifies your original mailbox. ## Faster on large mailboxes If your archive runs to several gigabytes, you’ll feel this one immediately. Searching is quicker, memory use is lower, and the interface no longer freezes when you open a very large message or run an export. Big Google Takeout `.mbox` files and multi-gigabyte Apple Mail exports stay responsive from the first click. ## More private by default Your email already never leaves your Mac — and 2.7.0 tightens privacy even further: - **Remote images (tracking pixels) are blocked more thoroughly**, so senders can’t quietly confirm you opened a message. - **Temporary files are cleaned up automatically**, leaving nothing behind on disk. - **New Settings** let you clear your search history and index cache whenever you want. ## Accessible to everyone Accessibility got a top-to-bottom pass in this release: - **Full VoiceOver and keyboard support**, so you can navigate the whole app without a mouse. - **Adjustable message text size and font**, plus **better contrast** for easier reading. - The **in-app language picker now lists all 18 languages**. ## Rock-solid with difficult files Real-world archives are messy. Mbox Viewer 2.7.0 now handles **malformed or oversized MBOX/EML files gracefully** instead of freezing or crashing, and when an **export or merge** can’t complete, you get a clear, specific message instead of a silent failure. ## HTML messages, leveled up HTML emails now show the **sender header and quick actions (Export, Print, Share) at the top** — exactly like plain-text messages. No more hunting for how to export a rich message; it’s right where you expect it. ## Still strictly read-only None of this changes the core promise: Mbox Viewer opens your archive **read-only**, works completely offline, and never writes to your original file. Even a single, irreplaceable `.mbox` is safe. You can read the full version history in the [changelog](https://mboxviewerpro.com/changelog/). [Get Mbox Viewer on the Mac App Store →](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `announcement` `product` `macos` `windows` # What's New in Mbox Viewer 2.8.2: Merging Mailboxes, Rebuilt Version 2.8.2 for Mac and Windows is all about merging mailboxes: Apple Mail exports are traceable again, the merge finally tells you what it is doing, and the toolbar explains itself. Still strictly read-only. [David Carrero](https://mboxviewerpro.com/author/) · August 7, 2026 **Mbox Viewer 2.8.2** has a single theme: merging mailboxes. It came out of a long, specific piece of feedback from someone who merges archives for a living, and every point in it turned out to be right. The Mac app (build 43) takes all eight; the Windows app takes the five that apply to it — one of them was already solved there back in 2.7.1, so on that point it is Mac catching up. The Mac one landed on the Mac App Store on 7 August and the Windows one on the Microsoft Store on the 8th: both are out. As always, the app is **read-only**. Merging writes a brand-new mailbox and never touches the files you feed it. ## Apple Mail exports are traceable again Merging has an optional setting that stamps each message with the mailbox it came from, using an `X-Mbox-Source` header. It is the answer to the obvious worry about merging: *if I combine ten archives, do I lose track of what came from where?* Except with Apple Mail exports, you did. “Export Mailbox…” doesn’t write a file called `Inbox.mbox` — it writes a *folder* called `Inbox.mbox` with a file inside it named, literally, `mbox`. That inner file is the one being read, so every message from every exported mailbox got tagged `X-Mbox-Source: mbox`. The header was there, it just said nothing. Merged messages now carry the name you actually recognize — `Inbox.mbox`, `Sent.mbox` — and two mailboxes that would end up with the same name are told apart by the folder above them: `Work/Inbox.mbox` and `Personal/Inbox.mbox`. This one is fixed in the shared engine, so both apps get exactly the same behaviour. ## Merging without opening a mailbox first (Mac) On the Mac, merge used to live inside a document window, which made for a strange dance: open a mailbox, choose Merge, then manually add that same mailbox to the list before adding the second one. You had to start from a file you didn’t necessarily care about. It is now an app-level action with its own window, in **File → Merge MBOX Files…** and as a button on the welcome screen, with nothing open. If you *do* have a mailbox open, it starts out in the list already. On Windows this has worked from the settings menu since 2.7.1, open mailbox included — here it’s the Mac that was behind. ## Knowing what the merge is doing Both apps used to go quiet exactly when you most wanted a sign of life. They fixed it in the shape each one needed. On the **Mac**, the whole window was rebuilt: the mailbox list scrolls instead of growing past the bottom of your screen, each mailbox shows its size with a running total (`2 mailboxes · 257 MB`), you can drop files straight onto it, and it reports real progress — `Merging 2 of 5 — Inbox.mbox`. When it finishes it says how it went in your own language (it used to report in English regardless) and swaps the buttons for **Show in Finder**, **Open Merged Mailbox** and **Close**. Before, there was no clear way out of a finished merge. On **Windows**, the progress bar was indeterminate with a fixed label, even though the engine had been reporting progress all along. It now names each mailbox as it goes — `Merging 2 of 5: Inbox.mbox`, the same name that gets written into the header — and when it’s done the status bar shows the **full path** of the merged file. Before, you only saw its name in the tab. ## Small things that added up The rest of the review went into details that each cost you a few seconds, over and over: - **Two Mac toolbar buttons looked identical.** Conversation threading and Search Filters shared an icon; threading now uses the conversation bubbles Mail uses for the same idea. - **Tooltips.** On the Mac, the six icon-only view buttons — Text, Full Headers, Properties, MIME, Raw, Hex — could only be decoded through the View menu; they now name themselves on hover, shortcut included: “Full Headers (⌘2)”. On Windows, fifteen controls had no explanation at all — the search box, the sort dropdown, the welcome-screen buttons, the viewer tabs, the buttons on each attachment — and Export and Print now show theirs too (Ctrl+E / Ctrl+P). - **Clicks that did nothing.** On the Mac, menu items that need an open mailbox are greyed out instead of silently ignoring the click. On Windows, the same for “Repair mailbox” and “Export repaired copy” in the settings menu — Merge stays available, because it works either way. - **Windows Help now explains merging**, in a new “Merge mailboxes” section: what “Remove duplicates” does, what the `X-Mbox-Source` checkbox writes, and how to actually see that header in a message. ## The same fix, upstream Mbox Viewer is built on [mboxShell](https://mboxviewerpro.com/mboxshell/), the open-source terminal tool at the heart of the app. The Apple Mail naming bug lived there too, and **mboxShell 0.6.2** fixes it in the same way — that is the engine the Windows app now ships. There’s also a documentation fix worth knowing if you use the CLI: `merge` deduplicates by default, and the real flag is `--no-dedup`. The `--dedup` flag the docs described never existed. ## Getting it 2.8.2 is out on both the Mac App Store and the Microsoft Store, where it arrives as a normal update. And if you’d rather read the full list first, it is on the [changelog](https://mboxviewerpro.com/changelog/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `announcement` `product` `windows` # Mbox Viewer for Windows 2.8.4 and 2.8.5: Exporting a Selection, and Printing That Finally Says Who Wrote Two updates in two days on the Microsoft Store: 2.8.4 exports your selection as a new MBOX and doubles the free plan to 1 GB; 2.8.5 fixes printing, which had been leaving out the subject, the date and the sender since the very first version. [David Carrero](https://mboxviewerpro.com/author/) · August 24, 2026 Two updates landed on the Microsoft Store in two days. **2.8.4** brings the Windows app level with the Mac one, and **2.8.5**, out the next day, fixes a printing defect that had been there since the first Windows release — reported by a customer through the [support form](https://mboxviewerpro.com/support/) and shipped the same day it was sent. The app is **read-only**, as always. Nothing below modifies the archive you open. ## Export your selection as a new MBOX Pick the messages that matter — by search, by Gmail label or one by one — and the app writes them into a brand-new MBOX containing only those. That is the delivery step of a legal hold or a public-records request: you narrow a 40 GB mailbox down to the three hundred messages that are actually in scope and produce a file with exactly those in it. The original archive is never modified — the export writes a new file beside it. ## The free plan goes from 500 MB to 1 GB Same app, same features, no time limit: twice the room before Pro comes into it. Pro remains a one-time purchase through the Microsoft Store that removes the size limit for good — no subscription, no account. ## Printing an email now carries its header Until 2.8.5, printing left out the subject, the date and who the message was from and to. Ctrl+P sent the message body to the printer on its own, because the app draws those fields in the interface, next to the body, where the print engine never sees them. The page began mid-message. What made it hard to spot: on a forwarded email the headers of the *quoted* message did come out, so it looked as though only the first one was missing. Printing now produces the same document as **Export → To PDF…**: subject, From, To, Cc and date at the top, separated from the body, and the attachment list at the foot. It was a Windows-only defect, present since the first version; macOS never had it. And a related one: messages with no subject can be printed too. The button used to check the subject to decide whether a message was selected, so with an empty one it simply did nothing. ## Ctrl+P now goes through your PDF viewer Ctrl+P opens the email as a PDF in your system viewer, and you print from there — with a real preview of what will come out of the printer, and the option to save the file or pass it on. That used to be handwork: export to PDF, find the file, open it. It is one step now. The content stays as sealed off as it is on screen: no JavaScript and not a single network request, printing included. ## Getting them Both arrive as normal updates from the Microsoft Store. The Mac app got the export and the 1 GB limit the same day as 2.8.4, along with an edition for schools — that one has [its own post](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-8-4-mac/). The full list, release by release, is on the [changelog](https://mboxviewerpro.com/changelog/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `announcement` `product` `macos` # What's New in Mbox Viewer 2.8.4 for Mac: Hand Over Only What Has To Be Handed Over Version 2.8.4 exports your selection as a brand-new MBOX, doubles the free plan to 1 GB and brings an edition for schools and universities. On the Mac App Store since 23 August. [David Carrero](https://mboxviewerpro.com/author/) · August 23, 2026 **Mbox Viewer 2.8.4** is out on the Mac App Store, and it closes a gap that had been open since the first version: you could read a huge archive, search it and print from it — but you could not take a handful of messages out of it. As always, the app is **read-only**. Nothing here modifies the archive you opened. ## Export your selection as a new MBOX Pick the messages that matter — by search, by Gmail label or one by one — and the app writes them into a brand-new MBOX that contains only those. That is the delivery step of a legal hold or a public-records request. The archive used to be something you looked at; what the other side actually asks for is *these messages, and nothing else*. Now you narrow a 40 GB mailbox down to the three hundred that are in scope and produce a file with exactly those in it, in a format anything can open. The original is never touched: the export writes a new file and leaves the archive exactly as it found it. It is the mirror image of merging, which has been there since 2.8.2 — one puts mailboxes together, the other takes a slice out. ## The free plan goes from 500 MB to 1 GB Same app, same features, no time limit — twice the room before Pro comes into it. If you tried Mbox Viewer with a Takeout export and bounced off the ceiling, the file that didn’t fit last month may well fit now. Pro is what it always was: a one-time in-app purchase that removes the size limit for good. No subscription, no account, no licence server. ## And an edition for schools and universities There is now a separate edition for institutions: **[Mbox Viewer Pro for Education](https://mboxviewerpro.com/education/)** — the same app with everything unlocked permanently, bought by the seat in Apple School Manager or Apple Business Manager and deployed by MDM. No in-app purchases to chase, no licence keys, no accounts and nothing that expires. ## Getting it 2.8.4 arrives as a normal update in the Mac App Store. The Windows app got the export and the 1 GB limit the same day, and a printing fix right after — that one has [its own post](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-8-4-and-2-8-5-windows/). The full list, release by release, is on the [changelog](https://mboxviewerpro.com/changelog/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `announcement` `product` `macos` `windows` # Mbox Viewer 2.8.6 for Mac and Windows: Gmail Labels Stop Being a Wall of Rows Nested Gmail labels now fold into a tree instead of a flat wall of near-identical rows, the annual subscription is back next to the lifetime licence, and Privacy can forget what you have opened. On the Microsoft Store since 4 September and the Mac App Store since the 7th, plus 2.8.7 for Windows. [David Carrero](https://mboxviewerpro.com/author/) · September 7, 2026 **2.8.6** is out on both stores: the Microsoft Store approved it on 4 September, the same day it was submitted, and Apple approved the Mac build on the 7th. Windows also got a small **2.8.7** on the 4th, which is why this post covers three release numbers at once. The app is **read-only**, as always. Nothing below modifies the archive you open. ## Gmail labels stop being a wall of rows Gmail keeps the hierarchy inside the label name. `Work/Clients/Acme` is *one* label, not three, and that is exactly how it lands in your Takeout export. The sidebar used to list those paths flat, so a mailbox with a real label tree turned into a column of rows that all began with the same words and differed at the end — the part you could not see. They now fold into a tree. Each row shows only its last segment, with the full path on hover; branches open and close, and the branch holding the label you are filtering by opens on its own. There is one detail worth knowing, because Gmail behaves the same way. A rung that exists only as a prefix — `Work/Clients/Acme` exists, but no message is labelled `Work/Clients` — is drawn greyed out and without a count. It groups and it unfolds, but it does not filter, because there is nothing to filter by. And if none of your labels contains a slash, the sidebar looks exactly as it did before. This one came from a customer who asked for it before buying. ## Two ways to have Pro The **annual subscription is on sale again**, next to Pro Lifetime. The upgrade screen shows both cards and you pick: pay once, or pay yearly. Either unlocks the same thing, and nothing changes for anyone who already bought the lifetime licence — that one is still a single payment and still does not expire. The subscription card is only drawn when the store hands the app a real price for it, so in a market where it is not on sale you get the screen you already know. The free tier is untouched: mailboxes up to 1 GB, every feature, no time limit. Prices for both plans, market by market, are on the [pricing page](https://mboxviewerpro.com/pricing/). That is also what **2.8.7 for Windows** is about. Settings used to tell someone paying the subscription that “Pro Lifetime” was active; now it simply says Pro is active. The licence state knows which of the two plans is behind it, and when both are present the lifetime one wins — that is the one you cannot lose. The wording is decided in a single place, so it also comes out right in the refresh that runs immediately after a purchase, not only when you reopen Settings. On the paywall, the one-time card now reads “One payment, forever” and drops the ”— no subscription” tail, which was redundant sitting right beside the subscription card. ## Privacy can forget what you have opened The search history can now be cleared from **Settings → Privacy**, and clearing it actually clears it. Every open window kept its own copy in memory and wrote it back on the next search, so what you had just deleted came straight back. It is a single list for the whole app now. On the Mac there is a third button. The app stores a bookmark for each mailbox you open, so it can reach the file again after a restart — and those bookmarks are keyed by full path, which means that together they are a list of the mailboxes you have opened. That button drops all of them. Nothing breaks: the next time you open a file, its bookmark is created again. The section also states plainly now that everything it lists stays on this Mac, and that clearing it cannot be undone. Worth saying, since this is the privacy section: the search indexes live in memory and there is no recent-files list, so the history was the only thing the app was keeping about your mail. ## The smaller fixes The file name proposed when you export a selection no longer eats the end of it. A Google Groups mailbox is named after the group — `my-group@googlegroups.com` — and the app was offering `my-group@googlegroups-selection.mbox`, because it trimmed anything after the last dot. The extension is now stripped only when it really is a mailbox one: `.mbox`, `.eml`, `.mbs`, `.mbx`. Verifying the new tree on Windows turned up two more: folding the branch that contained the active label used to drop the filter silently, and opening a branch could move the selection. And every link the app opens now points at **mboxviewerpro.com** — the website in About and Help, the privacy policy, and the marketing, support and privacy URLs in the store listing — opening the page in the language you are using the app in, instead of sending everyone to the English one. On the way there, a real bug turned up: the privacy link produced a 404 in Spanish, French, German and Portuguese, because the app built the address as `/es/privacy/` while the site translates the address too (`/es/privacidad/`, `/fr/confidentialite/`, `/de/datenschutz/`). Those four reach the real page now, and Polish was added alongside them. The old domain redirects, so nothing you had bookmarked stops working. ## Why the Mac jumps from 2.8.4 to 2.8.6 Because **2.8.5 was Windows-only**: a [printing fix](https://mboxviewerpro.com/blog/whats-new-in-mbox-viewer-2-8-4-and-2-8-5-windows/) that macOS never needed, shipped the same day it was reported. From here on the same number means the same thing on both platforms — 2.8.6 on Mac and 2.8.6 on Windows are the same release. ## Getting them Both arrive as ordinary updates from the Mac App Store and the Microsoft Store. The full list, release by release and platform by platform, is on the [changelog](https://mboxviewerpro.com/changelog/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `thunderbird` `mbox` `archives` # Where Thunderbird Keeps Your Email Thunderbird stores every folder as an MBOX file with no extension, inside a profile folder your system hides. Here is where to find it on Mac, Windows and Linux — and how to read that mail without Thunderbird installed. [David Carrero](https://mboxviewerpro.com/author/) · September 7, 2026 Thunderbird keeps your mail in a profile folder: `~/Library/Thunderbird/Profiles/` on macOS, `%APPDATA%\Thunderbird\Profiles\` on Windows, `~/.thunderbird/` on Linux. Inside it, every folder you see in the app — Inbox, Sent, Archives — is a single [MBOX](https://mboxviewerpro.com/glossary/mbox/) file with no extension at all. That is unusually good news, and most Thunderbird users never find out. Your mail is not locked in a proprietary database. It is sitting in standard files that plenty of software can read, including after Thunderbird is gone from the machine. ## Finding the profile The path has one unpredictable part: the profile folder has a random name, something like `x7k2p9qr.default-release`. Go to the Profiles folder and you will see it. - **macOS:** in Finder press `⌘⇧G` and paste `~/Library/Thunderbird/Profiles/` - **Windows:** press `Win + R`, paste `%APPDATA%\Thunderbird\Profiles` and hit Enter — this saves you from un-hiding `AppData`, which Windows keeps out of sight - **Linux:** `~/.thunderbird/` Inside the profile, mail lives in two places. `Mail/Local Folders/` holds anything stored on your machine, including POP accounts and folders you made yourself. `ImapMail/` holds the local copies of IMAP accounts, one directory per server. ## What the files look like Open `Mail/Local Folders/` and you get a list that confuses everyone the first time: ``` Archives Archives.msf Inbox Inbox.msf Sent Sent.msf ``` The files **with no extension** are your mail — each one a standard MBOX file, the whole folder in a single file. The `.msf` files next to them are Thunderbird’s own index (Mail Summary File), and you can ignore them completely: any reader worth using builds its own index and never needs them. If a folder has subfolders, they live in a directory with the same name plus `.sbd`. So `Archives.sbd/2019` is the mailbox for `Archives/2019`. ## Why is there no .mbox extension? Because Thunderbird never needed one. It knows what those files are from the folder they are in, so it never bothered to label them — which is fine until the day you want to open one somewhere else, and nothing on your computer recognizes a file called `Inbox` with no extension. You do not have to rename anything. [Mbox Viewer](https://mboxviewerpro.com/features/) opens an extension-less Thunderbird file directly: drag it onto the window, or use Open. If you would rather double-click, adding `.mbox` to a *copy* also works — but there is no need, and renaming the file Thunderbird is actively using is a bad habit. ## Reading it without Thunderbird This is the case that brings most people here: an old machine, a disk from someone who has died or left the company, a backup from a laptop that no longer boots. You have the profile folder and no working Thunderbird. Copy `Mail/Local Folders/` off the disk and open the files. That is all there is to it — no import, no account setup, no Thunderbird installation. On [Mac](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-mac/) and on [Windows](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-windows/) it is the same procedure, and the files are read-only: nothing gets written back. One caveat worth knowing: an IMAP folder under `ImapMail/` only contains what Thunderbird had actually downloaded. If the account was set to keep headers only, or to sync just the last few months, that is what you will find. The Local Folders are the complete ones. ## A word about compacting Thunderbird does not really delete messages when you delete them. It marks them and moves on, and the space is only reclaimed when the folder is [compacted](https://mboxviewerpro.com/glossary/compacting/). That is why an `Inbox` file can be 4 GB when the folder shows 800 MB of mail. Two consequences. If you are copying a profile for archiving, compacting first can make it dramatically smaller. And if you are looking for something that was deleted, an uncompacted file may still contain it — a reader that walks the raw file will show messages Thunderbird had already written off. ## If the file is enormous Thunderbird folders grow for years without anyone noticing, and a decade-old Inbox of several gigabytes is common. That size is fine for the format and hard on most readers, which load the whole file before showing anything. Mbox Viewer streams instead: a 50 GB mailbox of around half a million messages opens in under five minutes, stays below 600 MB of RAM, and re-opens in under a second afterwards thanks to its [binary index](https://mboxviewerpro.com/glossary/binary-index/). If your goal is to split a monster folder into manageable pieces rather than read it whole, we wrote about [that too](https://mboxviewerpro.com/blog/how-to-split-large-thunderbird-mbox-files/). --- Not sure what an MBOX file is in the first place? [Start here](https://mboxviewerpro.com/blog/what-is-an-mbox-file/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All posts](https://mboxviewerpro.com/blog/) `backup` `gmail` `privacy` # Why You Should Back Up Your Gmail Locally (and How) Cloud email is convenient until it isn't. Here's why keeping a local Gmail backup matters — account lockouts, accidental deletion, leaving providers — and how Mbox Viewer makes that archive usable. [David Carrero](https://mboxviewerpro.com/author/) · May 26, 2026 Most of us treat Gmail as permanent. It’s always there, always searchable, always synced. But “in the cloud” is not the same as “safe,” and email is often the single most important record we own — receipts, contracts, conversations, two-factor recovery codes, years of memories. This post makes the case for keeping a **local backup of your Gmail**, and shows how to make that backup actually useful. ## ”It’s in the cloud” is not a backup strategy Google’s infrastructure is excellent, but your *access* to it is fragile in ways that have nothing to do with their servers. ### Account lockouts happen People lose access to Google accounts more often than you’d think — a forgotten password, a lost phone with the only 2FA method, or an automated suspension flagged by mistake. When it happens, support can be slow or impossible to reach. If your mail lives only in that account, it’s gone the moment you’re locked out. ### Deletion is one click away A misfired filter, a “delete all” you didn’t mean, or a synced client gone wrong can wipe messages in seconds. Trash empties itself after 30 days. A local archive is the only copy that survives a bad click. ### You might leave (or be pushed off) Gmail Switching to a different provider, moving work email to a company domain, or a free account that gets retired — all of these can sever you from years of history. A local MBOX archive comes with you regardless. ### Compliance and records Freelancers and small businesses often need to keep email for tax, legal, or client-record reasons. An offline archive you control is far more dependable than hoping a cloud account stays open. ## What a good local backup looks like A useful backup has three properties: 1. **Open format.** It should not depend on any one vendor’s software to read. MBOX is plain text and will be readable for decades. 2. **Complete.** Headers, bodies, and attachments — not just a summary. 3. **Usable.** A 15 GB file you can’t open isn’t a backup; it’s a liability. The first two are easy: **Google Takeout** exports your entire Gmail to a standard MBOX file for free. The third is where most people get stuck. ## Where Mbox Viewer comes in A Takeout archive is only as good as your ability to read it. That’s exactly what [Mbox Viewer](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) is built for. - **Opens any size.** Streaming performance means even a multi-gigabyte Takeout file opens in seconds, with no import and no size cap. - **Searchable.** Find that one receipt from three years ago with operators like `from:`, `subject:`, and `has:attachment`. - **Exportable.** Pull specific messages out to EML or PDF, dump metadata to CSV, or extract every attachment in bulk. - **Private.** Everything runs locally on your Mac — no upload, no account, fully offline. Your backup stops being a file you’re afraid to touch and becomes a living archive you can actually use. ## A simple backup routine You don’t need anything elaborate. Twice a year: 1. Run **Google Takeout** and export **Mail** as a `.zip`. 2. Unzip it and move the `.mbox` file to an external drive or your regular backup. 3. Open it once in **Mbox Viewer** to confirm it’s complete and searchable. Ten minutes, twice a year, and your most important records are genuinely yours. ## Own your email Don’t wait for a lockout to wish you’d kept a copy. Export your Gmail and keep an archive you control. [Get Mbox Viewer on the Mac App Store →](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Attachment # Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. An attachment is a MIME part with a Content-Disposition header set to attachment, optionally including a filename parameter. The part's content is typically encoded with Base64 so that binary data can travel through text-based mail infrastructure. The Content-Type header identifies the file type, such as application/pdf or image/png, so the recipient's mail client knows how to handle it. Attachments are one of the most common reasons people search their email archives — locating a contract, an invoice, or a photo sent years ago. Filtering by has:attachment narrows results to messages that contain at least one attached file. Additional filters on filename or file type can narrow further, for example finding all messages with a PDF attachment from a specific sender. Mbox Viewer decodes MIME attachments and provides previews for common file types. It also supports batch export, allowing you to extract all attachments from a set of messages to a folder in one operation — useful when recovering files from a large archive without opening each message individually. ## Related terms [ MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. ](https://mboxviewerpro.com/glossary/mime/)[ Base64 A binary-to-text encoding scheme that represents arbitrary binary data using only 64 printable ASCII characters, widely used in email to safely transmit attachments and binary content. ](https://mboxviewerpro.com/glossary/base64/)[ Inline image An image embedded directly into an HTML email body using a Content-ID (cid:) reference, rather than attached as a separate downloadable file. The image data is stored as a MIME part within the same message. ](https://mboxviewerpro.com/glossary/inline-image/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Base64 # Base64 A binary-to-text encoding scheme that represents arbitrary binary data using only 64 printable ASCII characters, widely used in email to safely transmit attachments and binary content. Base64 (defined in RFC 4648) encodes every 3 bytes of binary input as 4 printable ASCII characters, chosen from the alphabet A–Z, a–z, 0–9, +, and /. Padding characters (=) are added if the input length is not a multiple of 3. The result is about 33% larger than the original data but contains no characters that could be misinterpreted by text-based mail transport systems. In MIME email, Base64 is the standard transfer encoding for attachments and binary content. The Content-Transfer-Encoding header is set to base64, and the encoded data appears in the message body in lines of up to 76 characters. When a mail client downloads the message, it decodes the Base64 data back to the original binary before presenting it to the user. Base64 is also used to encode inline images and, in some cases, HTML bodies or text with heavy use of non-ASCII characters. An email reader must decode Base64 parts transparently so the user sees the original content rather than the encoded ASCII text. Mbox Viewer decodes Base64 as part of its MIME processing pipeline. ## Related terms [ Quoted-printable A MIME transfer encoding that represents text with mostly ASCII characters, escaping non-ASCII bytes as =XX hex sequences. It keeps the majority of the text human-readable in the raw message source. ](https://mboxviewerpro.com/glossary/quoted-printable/)[ Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. ](https://mboxviewerpro.com/glossary/attachment/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Binary index # Binary index A compact index file that Mbox Viewer writes alongside an MBOX archive after the first parse, storing message byte offsets and metadata to enable near-instant reopens without re-scanning the entire file. After Mbox Viewer opens and streams through an MBOX file for the first time, it writes a small binary index file to the same location. This index records the byte offset and length of each message in the MBOX, along with key header metadata such as date, sender, and subject. On all subsequent opens, the app loads the index rather than re-scanning the file, reducing open time from minutes (for very large archives) to under a second. To ensure the index stays valid, Mbox Viewer stores a SHA-256 hash of the MBOX file (or a portion of it sufficient to detect changes) in the index. When the app opens an MBOX file, it verifies that the hash matches before trusting the index. If the MBOX has been modified — for example, because a new export replaced the old file — the index is discarded and the file is re-parsed. The binary index is a performance optimization that is entirely transparent to the user. It never modifies the MBOX file itself; it only creates a companion file. This is consistent with Mbox Viewer's read-only design: your email archive is never altered, only read. ## Related terms [ Streaming parser A parsing technique that reads a file incrementally in small chunks rather than loading the entire file into memory at once, enabling tools to open and index very large MBOX files — tens or hundreds of gigabytes — with low memory usage. ](https://mboxviewerpro.com/glossary/streaming-parser/)[ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Charset # Charset The character encoding that specifies how bytes in a text part are mapped to readable characters. Common charsets include UTF-8, ISO-8859-1, and Shift\_JIS; a mismatch causes garbled text known as mojibake. Every text part of an email has a character encoding — a rule that maps byte values to characters. The charset is declared in the Content-Type header, for example: Content-Type: text/plain; charset="UTF-8". UTF-8 is the dominant encoding today because it can represent every character in Unicode, but older messages may use regional encodings such as ISO-8859-1 (Western European), ISO-2022-JP (Japanese), GB2312 (Simplified Chinese), or Windows-1252. When an email is displayed with the wrong charset, characters outside the basic ASCII range are rendered as nonsense symbols — a phenomenon known as mojibake (from Japanese, roughly "character transformation"). This happens when a message declares one charset but the reader uses another, or when no charset is declared and the reader guesses incorrectly. Mbox Viewer detects the charset declaration from the MIME headers and applies the correct decoder for each message part. For messages that omit a charset declaration, the app applies heuristic detection to identify the encoding from the byte patterns, reducing mojibake in archives that contain mail from older or non-standard clients. ## Related terms [ Encoded-word (RFC 2047) An encoding scheme defined in RFC 2047 ("Encoded-Word") that allows non-ASCII characters in email header fields such as Subject and From, by encoding them as =?charset?encoding?text?= tokens. ](https://mboxviewerpro.com/glossary/rfc2047/)[ MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. ](https://mboxviewerpro.com/glossary/mime/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Compacting # Compacting X-Mozilla-Status The operation that actually removes deleted messages from an mbox file. Until it runs, a deleted message is only marked as deleted — it is still in the file, and still readable. Thunderbird and other mbox-based clients do not rewrite a whole mailbox every time you delete a message; that would be far too slow. Instead they set a flag in the message's headers — X-Mozilla-Status and X-Mozilla-Status2 — marking it deleted, and move on. The bytes stay exactly where they were. Compacting is the separate step that rewrites the file without the flagged messages and reclaims the space. This explains a common surprise: a folder that shows four thousand messages occupying nine gigabytes on disk. The difference is deleted mail that has never been compacted away. It also explains why a mailbox copied out of a profile can show messages the owner believes were deleted long ago — an external reader has no reason to honour a flag Thunderbird invented. Before splitting, copying or handing over a mailbox, it is worth deciding deliberately which behaviour you want: compact first if those messages should not travel with the file, or skip it knowingly if they are part of what you mean to preserve. Either way, count the messages afterwards so you know what you actually have. ## Related terms [ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ Deduplication The process of detecting and removing duplicate email messages from an archive, typically by comparing Message-ID values, to avoid redundancy when merging multiple MBOX files. ](https://mboxviewerpro.com/glossary/deduplication/)[ Streaming parser A parsing technique that reads a file incrementally in small chunks rather than loading the entire file into memory at once, enabling tools to open and index very large MBOX files — tens or hundreds of gigabytes — with low memory usage. ](https://mboxviewerpro.com/glossary/streaming-parser/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Deduplication # Deduplication The process of detecting and removing duplicate email messages from an archive, typically by comparing Message-ID values, to avoid redundancy when merging multiple MBOX files. Duplicate messages arise naturally when managing email archives over time. For example, if you run two Google Takeout exports six months apart and combine them, messages from the overlapping period will appear in both MBOX files. Merging without deduplication doubles those messages in the combined archive, breaking thread counts and search result relevance. The most reliable deduplication key is the Message-ID header, which is designed to be globally unique per message. Two messages with the same Message-ID are considered duplicates. A deduplication pass over a set of MBOX files can identify these collisions and either skip the duplicate during import or remove it from the merged output. Edge cases in deduplication include messages with missing Message-IDs (common in very old or malformed mail) and messages with identical Message-IDs but different content (caused by buggy sending software). Robust tools handle these by combining Message-ID with a hash of key headers or the full message body as a secondary fingerprint. Mbox Viewer uses Message-ID comparison when merging archives to keep the result clean. ## Related terms [ Message-ID A globally unique identifier assigned to each email message, specified in the Message-ID header. It is used to track messages, build conversation threads, and detect duplicates when merging archives. ](https://mboxviewerpro.com/glossary/message-id/)[ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) SPF, DKIM and DMARC # SPF, DKIM and DMARC SPF · DKIM · DMARC The three mechanisms that establish whether a message really came from the domain it claims: SPF authorises sending servers, DKIM signs the message cryptographically, and DMARC ties the two to a published policy. SPF (Sender Policy Framework) is a DNS record listing which servers may send mail for a domain; the receiving server checks the connecting address against that list. DKIM (DomainKeys Identified Mail) goes further: the sending domain signs the body and a chosen set of headers with a private key and adds a DKIM-Signature header, which anyone can verify against the public key published in DNS. DMARC sits on top, telling receivers what to do when those checks fail and requiring the authenticated domain to match the visible From: address. In an archived mailbox the practical trace of all this is the Authentication-Results header, written by the receiving server at the moment of delivery. It records the verdict that was reached then — pass, fail or none — which is precisely the point: it captures what was known when the message arrived. A DKIM signature can in principle be re-verified years later, but only while the domain still publishes the matching public key, and operators rotate those keys routinely. So a signature that no longer verifies is not evidence of tampering: it is often just an expired key. That nuance matters whenever archived mail is offered as proof of anything. ## Related terms [ Header The structured metadata block at the beginning of an email message, containing fields like From, To, Subject, Date, and numerous technical fields that describe how the message was composed, routed, and encoded. ](https://mboxviewerpro.com/glossary/header/)[ Received The header each mail server adds as a message passes through it. Read from the bottom up, the Received lines reconstruct the route a message actually travelled. ](https://mboxviewerpro.com/glossary/received/)[ eDiscovery The legal process of identifying, preserving, reviewing and handing over electronic records — email above all. It is the reason most people ever need to cut a mailbox down to a specific set of messages. ](https://mboxviewerpro.com/glossary/ediscovery/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) eDiscovery # eDiscovery legal hold · disclosure The legal process of identifying, preserving, reviewing and handing over electronic records — email above all. It is the reason most people ever need to cut a mailbox down to a specific set of messages. When a dispute, an investigation or a public-records request arrives, the parties must produce the relevant electronic communications. A legal hold usually comes first, freezing deletion so nothing disappears while the matter is live. Then comes the narrowing: from an entire mailbox down to the messages that fall within the agreed date range, custodians and topics. For email this is a practical, unglamorous job. The archive has to be searched, the relevant messages selected, and a new file produced holding only those — because handing over an entire mailbox usually discloses far more than the request asked for. Message counts, date ranges and deduplication all have to hold up, since the other side may check them. It is the workflow behind Mbox Viewer's export of a selection as a new MBOX: filter a large archive, select what belongs in the response, and write a mailbox containing exactly that, with the source file never modified. (Nothing here is legal advice — the standards that apply to a given matter are for the lawyers on it.) ## Related terms [ Google Vault Google Workspace's retention and eDiscovery tool. An administrator can hold, search and export the mail of accounts across an organisation — and the export is MBOX. ](https://mboxviewerpro.com/glossary/google-vault/)[ SPF, DKIM and DMARC The three mechanisms that establish whether a message really came from the domain it claims: SPF authorises sending servers, DKIM signs the message cryptographically, and DMARC ties the two to a published policy. ](https://mboxviewerpro.com/glossary/dkim/)[ Deduplication The process of detecting and removing duplicate email messages from an archive, typically by comparing Message-ID values, to avoid redundancy when merging multiple MBOX files. ](https://mboxviewerpro.com/glossary/deduplication/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) EML # EML A single-message file in MIME format, containing headers, body, and attachments. EML files are widely supported across email clients and are useful for archiving or sharing individual messages. EML is a plain-text file format defined by RFC 5322 that holds exactly one email message. The file begins with header fields — From, To, Subject, Date, and various technical headers — followed by a blank line and then the message body. If the message has attachments or an HTML version, those are encoded as MIME parts within the same file. Because the format is an open standard, EML files open in most email clients on any operating system: Thunderbird, Apple Mail, Outlook, and many others can import or display them directly. This portability makes EML a practical choice for archiving individual messages or sharing them outside of a mail service. When working with large collections of EML files, searching across all of them at once is the main challenge. Mbox Viewer can open individual EML files and apply the same full-text and metadata search capabilities it provides for MBOX archives, allowing you to locate messages by sender, date range, subject, or attachment name. ## Related terms [ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ MSG Microsoft Outlook's proprietary binary format for a single email message, storing headers, body, and attachments in a Compound Document Structure. Unlike EML, MSG is not a plain-text standard. ](https://mboxviewerpro.com/glossary/msg/)[ MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. ](https://mboxviewerpro.com/glossary/mime/)[ EMLX Apple Mail's per-message file format: one message per file, prefixed by its byte length and followed by an XML property list of Apple's own metadata. ](https://mboxviewerpro.com/glossary/emlx/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) EMLX # EMLX Apple Mail Apple Mail's per-message file format: one message per file, prefixed by its byte length and followed by an XML property list of Apple's own metadata. Apple Mail stores each message as its own .emlx file. The structure is unusual but simple: the first line is a number — the byte length of the message that follows — then the message itself in standard RFC 5322 form, and finally an XML plist holding Apple's metadata, such as flags, mailbox identifiers and conversation information. Strip the first line and the plist and you are left with an ordinary EML file. You will also meet .partial.emlx files. These belong to messages whose attachments were never downloaded from the server, so the file contains the headers and body but only placeholders where the attachments should be. If the account is gone, so are those attachments — a good reason to check before decommissioning an old mail account. When Apple Mail exports a mailbox it does not produce .emlx at all: it writes a folder named Inbox.mbox containing a file literally called mbox, which is standard MBOX. Mbox Viewer resolves that package automatically and names the mailbox after the folder, so you see Inbox.mbox rather than a bare mbox. ## Related terms [ EML A single-message file in MIME format, containing headers, body, and attachments. EML files are widely supported across email clients and are useful for archiving or sharing individual messages. ](https://mboxviewerpro.com/glossary/eml/)[ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. ](https://mboxviewerpro.com/glossary/attachment/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Envelope # Envelope The delivery metadata used by SMTP servers to route an email message — specifically the envelope sender (MAIL FROM) and envelope recipients (RCPT TO) — which may differ from the visible From and To headers. In email terminology, the "envelope" borrows from the analogy of a postal envelope: it contains the routing information used by the mail infrastructure to deliver the letter, separate from what is written on the letter inside. The SMTP envelope consists of the MAIL FROM address (the Return-Path) and one or more RCPT TO addresses that tell each server where to deliver the message. Envelope addresses are not always the same as the header From and To fields. A mailing list, for example, might have an envelope sender of list-bounces@example.com so that undeliverable messages return to the list manager, while the From header shows the original poster's address. The envelope sender is preserved in the Return-Path header after delivery. In MBOX files, the "From " separator line that begins each message contains the envelope sender address and a timestamp, recorded by the receiving mail server. This line is technically part of the MBOX format rather than the message itself, but it provides useful delivery metadata alongside the message headers. ## Related terms [ Header The structured metadata block at the beginning of an email message, containing fields like From, To, Subject, Date, and numerous technical fields that describe how the message was composed, routed, and encoded. ](https://mboxviewerpro.com/glossary/header/)[ SMTP Simple Mail Transfer Protocol — the standard protocol used to send and relay email messages between mail servers. It is used for outgoing mail only; reading email requires IMAP or POP3. ](https://mboxviewerpro.com/glossary/smtp/)[ mboxrd / mboxo The MBOX family's variants, which differ in how they protect body lines that begin with "From ". mboxrd escapes them reversibly; mboxo does not; mboxcl and mboxcl2 use a Content-Length header instead. ](https://mboxviewerpro.com/glossary/mboxrd/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Gmail labels # Gmail labels labels Gmail's tagging system that assigns one or more labels to each message, serving the role that folders play in traditional email clients. A single message can carry multiple labels simultaneously. Unlike traditional email clients that organize messages into exclusive folders, Gmail uses labels — essentially tags that can be applied to any message in any combination. A message can be in Inbox, starred, and also tagged with a custom label such as "Receipts" at the same time. System labels like Sent, Drafts, Spam, and Trash are also implemented as labels internally. When Google Takeout exports Gmail, it encodes label information in the MBOX file using a non-standard X-Gmail-Labels header on each message. This header contains a comma-separated list of all labels applied to that message. Standard MBOX readers that do not understand this header will still display the messages but will lose the label organization. Mbox Viewer reads the X-Gmail-Labels header and reconstructs the label hierarchy in the sidebar, allowing you to browse your archive by label just as you would in Gmail. You can also search by label using the label: filter, or combine it with other criteria such as from:, subject:, or date ranges to narrow results in large archives. ## Related terms [ Google Takeout Google's official service for exporting your personal data, including Gmail. For email, it produces one or more MBOX files containing all your messages and their Gmail labels. ](https://mboxviewerpro.com/glossary/google-takeout/)[ Threading (JWZ) The process of grouping related email messages into conversations by following In-Reply-To and References header links, typically using the JWZ algorithm that supports up to four levels of nesting. ](https://mboxviewerpro.com/glossary/threading/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Google Takeout # Google Takeout Google's official service for exporting your personal data, including Gmail. For email, it produces one or more MBOX files containing all your messages and their Gmail labels. Google Takeout (takeout.google.com) lets any Google account holder download a copy of their data from Google's services — Gmail, Google Drive, Photos, Contacts, and many others. For Gmail, Takeout exports messages as MBOX files, preserving the full message content, headers, and label information. Depending on mailbox size, Google may split the export into multiple MBOX files or offer different size limits per file. The export process typically takes from a few minutes to several hours or even days for very large mailboxes. Google sends an email notification when the archive is ready to download. The resulting MBOX files are a complete, offline copy of your Gmail that you own independently of Google's servers. Once downloaded, you can open the MBOX files in any compatible application. Mbox Viewer is designed specifically for this use case: it opens the MBOX files from Google Takeout without any import step, streams through files of any size, and reconstructs the Gmail label hierarchy in the sidebar so you can navigate your archive just as you would in Gmail. ## Step-by-step guides - [ How to Export Gmail with Google Takeout (and Open It on Mac) A step-by-step guide to exporting your Gmail to an MBOX file with Google Takeout, downloading it safely, and opening it instantly in Mbox Viewer on macOS. ](https://mboxviewerpro.com/guides/how-to-export-gmail-with-google-takeout/) - [ How to Open a Gmail (Google Takeout) MBOX File on Windows Downloaded your Gmail with Google Takeout and got a giant .mbox inside a ZIP? Here's how to unzip it on Windows and open the mailbox with Mbox Viewer — no import, no Gmail login. ](https://mboxviewerpro.com/guides/how-to-open-gmail-takeout-mbox-on-windows/) ## Related terms [ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ Gmail labels Gmail's tagging system that assigns one or more labels to each message, serving the role that folders play in traditional email clients. A single message can carry multiple labels simultaneously. ](https://mboxviewerpro.com/glossary/gmail-labels/)[ Google Vault Google Workspace's retention and eDiscovery tool. An administrator can hold, search and export the mail of accounts across an organisation — and the export is MBOX. ](https://mboxviewerpro.com/glossary/google-vault/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Google Vault # Google Vault Google Workspace's retention and eDiscovery tool. An administrator can hold, search and export the mail of accounts across an organisation — and the export is MBOX. Vault is the administrative counterpart to Google Takeout. Where Takeout lets a person download their own data, Vault lets an organisation set retention rules, place legal holds, search across many accounts at once and export what it finds. It is part of Google Workspace, not of consumer Gmail accounts. Mail exported from Vault arrives as MBOX, accompanied by metadata files that describe the export itself. The mailboxes open in any standard reader, which is what makes Vault exports workable outside Google — an important detail when the recipient is a lawyer or an external investigator with no access to the domain. One difference from a Takeout export is worth knowing in advance: a Vault export does not carry Gmail labels. Anything you would normally filter by label has to be found by search, date or sender instead — which is exactly why exporting a chosen selection, rather than a whole label, is the workflow that fits this material. ## Related terms [ Google Takeout Google's official service for exporting your personal data, including Gmail. For email, it produces one or more MBOX files containing all your messages and their Gmail labels. ](https://mboxviewerpro.com/glossary/google-takeout/)[ eDiscovery The legal process of identifying, preserving, reviewing and handing over electronic records — email above all. It is the reason most people ever need to cut a mailbox down to a specific set of messages. ](https://mboxviewerpro.com/glossary/ediscovery/)[ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Header # Header The structured metadata block at the beginning of an email message, containing fields like From, To, Subject, Date, and numerous technical fields that describe how the message was composed, routed, and encoded. Every email message consists of two parts separated by a blank line: the header section and the body. The header is a series of name-value pairs, one per line, each following the format "Field-Name: value". RFC 5322 defines the syntax and the meaning of common fields. Headers accumulate as a message travels: each mail server adds a Received header, creating a traceable delivery chain. User-facing fields like From, To, Cc, Subject, and Date are the most recognizable headers, but there are dozens of technical fields as well: Content-Type describes the body encoding, MIME-Version signals multi-part structure, Message-ID provides a globally unique identifier, and X- prefixed fields carry vendor-specific metadata (such as Gmail's X-Gmail-Labels). Headers are the primary data source for sorting, filtering, and searching email. Mbox Viewer parses headers for every message in an MBOX file to populate the column list — sender, recipient, subject, date — and to build the full-text index. Searching with filters like from:alice@example.com or subject:invoice targets header fields directly. ## Related terms [ MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. ](https://mboxviewerpro.com/glossary/mime/)[ Message-ID A globally unique identifier assigned to each email message, specified in the Message-ID header. It is used to track messages, build conversation threads, and detect duplicates when merging archives. ](https://mboxviewerpro.com/glossary/message-id/)[ Envelope The delivery metadata used by SMTP servers to route an email message — specifically the envelope sender (MAIL FROM) and envelope recipients (RCPT TO) — which may differ from the visible From and To headers. ](https://mboxviewerpro.com/glossary/envelope/)[ Received The header each mail server adds as a message passes through it. Read from the bottom up, the Received lines reconstruct the route a message actually travelled. ](https://mboxviewerpro.com/glossary/received/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) HTML email # HTML email An email message whose body is formatted with HTML and CSS, allowing rich typography, layout, colors, and images. Most modern email is HTML, but privacy and security considerations require careful rendering. HTML email uses a Content-Type of text/html and applies HTML markup and inline CSS to produce formatted messages with headings, bold text, colored backgrounds, images, and links. Because email clients render HTML in highly varied environments — from mobile apps to desktop clients to web browsers — HTML email is typically written with inline styles and simplified markup to maximize compatibility. HTML email introduces privacy and security concerns that plain-text email does not. Remote images (fetched over HTTP when the message is opened) can act as tracking pixels, revealing when you read a message and your approximate location. Malicious messages can attempt to inject scripts or misleading links. Email clients typically block remote images by default and sanitize HTML to remove scripts and dangerous tags. Mbox Viewer renders HTML email in a sandboxed view that blocks all external network requests, preventing tracking pixels and protecting privacy. The HTML is sanitized before rendering to remove potentially harmful elements. Inline images stored as MIME parts (cid: references) are displayed normally, since they require no network access. ## Related terms [ Inline image An image embedded directly into an HTML email body using a Content-ID (cid:) reference, rather than attached as a separate downloadable file. The image data is stored as a MIME part within the same message. ](https://mboxviewerpro.com/glossary/inline-image/)[ MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. ](https://mboxviewerpro.com/glossary/mime/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) IMAP # IMAP Internet Message Access Protocol — the standard protocol for accessing email stored on a server, keeping messages synchronized across multiple devices without downloading and deleting them. IMAP (Internet Message Access Protocol, RFC 9051) is the protocol that modern email clients use to connect to mail servers such as Gmail, Outlook.com, and corporate Exchange servers. Unlike its predecessor POP3, IMAP keeps messages on the server and synchronizes the client's view of the mailbox, so the same messages appear consistently whether you read them on a phone, a laptop, or the web. Gmail exposes its mailbox structure over IMAP, mapping labels to IMAP folders. This means any standard IMAP client can access Gmail, though Gmail-specific features such as threaded conversations are not part of the IMAP standard. When you want a fully offline, searchable copy of your IMAP mailbox, the most common approach is to use a client like Thunderbird to download everything and then export to MBOX. IMAP is a live connection protocol, not an archival format. For long-term preservation of email, exporting to MBOX or EML is recommended, because those formats do not depend on a server being available. Google Takeout automates this export step for Gmail users. ## Related terms [ POP3 Post Office Protocol 3 — an older email retrieval protocol that downloads messages from a server to a local device, typically removing them from the server afterward. ](https://mboxviewerpro.com/glossary/pop3/)[ SMTP Simple Mail Transfer Protocol — the standard protocol used to send and relay email messages between mail servers. It is used for outgoing mail only; reading email requires IMAP or POP3. ](https://mboxviewerpro.com/glossary/smtp/)[ Maildir A mailbox format that stores each email message as a separate file within a directory hierarchy, rather than concatenating all messages into a single file like MBOX. ](https://mboxviewerpro.com/glossary/maildir/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) In-Reply-To / References # In-Reply-To / References Email headers (In-Reply-To and References) that link a reply to the message it responds to, enabling mail clients and archive tools to group related messages into conversation threads. When you reply to an email, your mail client sets two headers in the outgoing message: In-Reply-To contains the Message-ID of the single message you are directly replying to, while References contains the full chain of Message-IDs from the entire conversation up to that point. Together they form the explicit link graph that threading algorithms use to reconstruct conversations. The JWZ threading algorithm (named after Jamie Zawinski, who described it for Netscape Mail) uses In-Reply-To and References to build a tree of messages. Messages without explicit references can be matched heuristically by Subject (stripping Re: and Fwd: prefixes) as a fallback. The result is a grouped view where all messages in a conversation appear together regardless of the order they arrived. In-Reply-To and References are critical for navigating large archives. Without thread reconstruction, a mailbox with thousands of messages is a flat chronological list; with threading, related messages collapse into conversations that are much easier to scan. Mbox Viewer reconstructs threads from these headers when displaying MBOX archives. ## Related terms [ Message-ID A globally unique identifier assigned to each email message, specified in the Message-ID header. It is used to track messages, build conversation threads, and detect duplicates when merging archives. ](https://mboxviewerpro.com/glossary/message-id/)[ Threading (JWZ) The process of grouping related email messages into conversations by following In-Reply-To and References header links, typically using the JWZ algorithm that supports up to four levels of nesting. ](https://mboxviewerpro.com/glossary/threading/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Inline image # Inline image CID An image embedded directly into an HTML email body using a Content-ID (cid:) reference, rather than attached as a separate downloadable file. The image data is stored as a MIME part within the same message. Inline images use the multipart/related MIME structure. The HTML body part references an image with a src attribute like src="cid:image001@example.com", and a corresponding MIME part in the same message carries the actual image data with a Content-ID header of . This allows formatted emails to include logos, diagrams, or decorative images that appear embedded in the layout without requiring the recipient to be online. Inline images differ from remote images, which use normal HTTP URLs (src="https://example.com/logo.png") and are fetched from an external server when the message is opened. Remote images are a known privacy concern because the server can track when and by whom the image was requested (a "tracking pixel" technique). Privacy-conscious mail clients block remote images by default. Mbox Viewer displays inline images by resolving cid: references to the corresponding MIME parts within the message, so formatted emails render correctly in offline viewing. Remote images are blocked to protect privacy, consistent with the app's local-only, read-only design. ## Related terms [ Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. ](https://mboxviewerpro.com/glossary/attachment/)[ HTML email An email message whose body is formatted with HTML and CSS, allowing rich typography, layout, colors, and images. Most modern email is HTML, but privacy and security considerations require careful rendering. ](https://mboxviewerpro.com/glossary/html-email/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Maildir # Maildir A mailbox format that stores each email message as a separate file within a directory hierarchy, rather than concatenating all messages into a single file like MBOX. Maildir was introduced by qmail and is now used by many Unix/Linux mail servers including Dovecot and Courier. In the Maildir layout, each message lives as its own file inside one of three subdirectories — new, cur, and tmp — with additional subdirectories representing folders or labels. This per-file design eliminates locking issues that can affect MBOX files when multiple processes access the mailbox simultaneously. Because every message is a discrete file, Maildir makes it easy to add, delete, or move individual messages without touching other messages. However, managing a mailbox with hundreds of thousands of files means that filesystem performance on some operating systems can become a bottleneck, and tools designed for MBOX may not read Maildir directly. Converting a Maildir archive to MBOX is a common step before importing mail into tools or services that expect MBOX input. Standard utilities such as mb2md, or scripts using formail, can perform this conversion. Google Takeout produces MBOX rather than Maildir, so users downloading Gmail archives will work with MBOX files directly. ## Related terms [ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ IMAP Internet Message Access Protocol — the standard protocol for accessing email stored on a server, keeping messages synchronized across multiple devices without downloading and deleting them. ](https://mboxviewerpro.com/glossary/imap/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) MBOX # MBOX .mbox · mbox file · mailbox file A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. MBOX (short for mailbox) is one of the oldest and most widely supported email storage formats. Every message is appended one after another in a single text file, with each message separated from the next by a line that starts with "From " (note the trailing space) followed by the sender address and a timestamp. Because the entire archive lives in a single file, MBOX is easy to copy, compress, and store as a long-term backup. Google Takeout produces MBOX files when you export Gmail data, sometimes splitting very large mailboxes into multiple files. Other services and desktop clients — Apple Mail, Thunderbird, Postfix — also use MBOX variants (mboxo, mboxrd, mboxcl2), which differ mainly in how they escape embedded "From " lines within message bodies. Opening a large MBOX file without a specialized tool can be slow because most programs parse the entire file before showing any messages. Mbox Viewer addresses this with a streaming parser that reads the file incrementally and a binary index that enables subsequent opens in under a second, regardless of file size. One last thing, because it sends people to the wrong place: the name collides with things that have nothing to do with email. Makita's M-Box is a stackable tool case, and the Ford Thunderbird is a car — while Thunderbird, the Mozilla email client, does store its mail in MBOX files. If you got here after downloading something ending in .mbox from Google, Apple Mail or Thunderbird, you are in the right place: it is a mailbox, and it is plain text. ## Step-by-step guides - [ How to Open an MBOX File on Mac (Even Huge Ones) Three ways to open an MBOX file on macOS — Apple Mail, Thunderbird or a dedicated viewer — with the steps for each, and which one to pick for a multi-gigabyte Gmail archive. ](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/) - [ How to Open an MBOX File on Windows 10 and 11 Three ways to open and read an MBOX file on Windows: import it into Thunderbird, open it with a dedicated viewer, or take a quick look. Steps for each, and which one fits your file. ](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/) ## Related terms [ EML A single-message file in MIME format, containing headers, body, and attachments. EML files are widely supported across email clients and are useful for archiving or sharing individual messages. ](https://mboxviewerpro.com/glossary/eml/)[ Maildir A mailbox format that stores each email message as a separate file within a directory hierarchy, rather than concatenating all messages into a single file like MBOX. ](https://mboxviewerpro.com/glossary/maildir/)[ Google Takeout Google's official service for exporting your personal data, including Gmail. For email, it produces one or more MBOX files containing all your messages and their Gmail labels. ](https://mboxviewerpro.com/glossary/google-takeout/)[ mboxrd / mboxo The MBOX family's variants, which differ in how they protect body lines that begin with "From ". mboxrd escapes them reversibly; mboxo does not; mboxcl and mboxcl2 use a Content-Length header instead. ](https://mboxviewerpro.com/glossary/mboxrd/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) mboxrd / mboxo # mboxrd / mboxo From-quoting · mboxcl2 The MBOX family's variants, which differ in how they protect body lines that begin with "From ". mboxrd escapes them reversibly; mboxo does not; mboxcl and mboxcl2 use a Content-Length header instead. In an MBOX file, a line starting with "From " marks the beginning of a new message. That creates an obvious problem: what if a message body contains such a line, in a quoted reply or a code sample? The variants of the format are the different answers to that question. mboxo prefixes the offending line with a > character. mboxrd does the same but also escapes lines that already begin with >From, adding another >, which makes the transformation reversible — you can always recover the original text. mboxcl and mboxcl2 take another route entirely, recording each message's length in a Content-Length header. This matters more than it sounds, because not every program that ever wrote your mailbox followed the rules. A file may well contain an unescaped body line starting with "From ". Any tool that splits an archive by searching for that pattern will tear such a message in two, turning one email into two half-emails without warning. It is the main reason to treat mbox files as mail rather than as text: parse them, select whole messages, and check that the message count before and after a split still matches. Mbox Viewer and mboxShell read every variant of the family, so you do not need to know which one produced your file. ## Related terms [ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ Envelope The delivery metadata used by SMTP servers to route an email message — specifically the envelope sender (MAIL FROM) and envelope recipients (RCPT TO) — which may differ from the visible From and To headers. ](https://mboxviewerpro.com/glossary/envelope/)[ MBX (Eudora) Eudora's mailbox file: plain mbox under a different extension, paired with a .toc index file. Readable today with no conversion — but its attachments were stored outside the mailbox. ](https://mboxviewerpro.com/glossary/mbx/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) MBX (Eudora) # MBX (Eudora) TOC · Eudora Eudora's mailbox file: plain mbox under a different extension, paired with a .toc index file. Readable today with no conversion — but its attachments were stored outside the mailbox. Eudora, the email client that dominated the early internet, stored each mailbox as a plain-text file with an .mbx extension: messages one after another, each starting with a "From " envelope line, exactly like MBOX. Beside it sat a .toc file holding Eudora's own table of contents — message positions, read state, sizes. The .toc is not needed to read the mail; it can be ignored or lost without consequence. One quirk surprises people opening these files today: Eudora usually wrote the envelope line as "From ???@???" instead of a real address, filling in a placeholder. It looks alarming and changes nothing — the real sender is in the From: header, where any parser that reads headers rather than guessing from the envelope will find it. The genuine gap is attachments. Eudora detached them, writing each one into a separate attachments folder and leaving a line in the message body reading Attachment Converted: followed by a path. A recovered .mbx therefore shows attachments as references, not files, unless that folder was kept too — so copy the whole Eudora directory, not just the mailboxes. Mbox Viewer registers .mbx (and .mbs) alongside .mbox, so these files open with a double-click, no renaming required. ## Related terms [ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ mboxrd / mboxo The MBOX family's variants, which differ in how they protect body lines that begin with "From ". mboxrd escapes them reversibly; mboxo does not; mboxcl and mboxcl2 use a Content-Length header instead. ](https://mboxviewerpro.com/glossary/mboxrd/)[ Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. ](https://mboxviewerpro.com/glossary/attachment/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Message-ID # Message-ID A globally unique identifier assigned to each email message, specified in the Message-ID header. It is used to track messages, build conversation threads, and detect duplicates when merging archives. The Message-ID header (RFC 5322 section 3.6.4) contains a string that is intended to be unique across all email ever sent, typically formatted as a local-part@domain string such as . The sending mail server generates this identifier at the moment of transmission. Replies include the original message's Message-ID in their In-Reply-To and References headers to link the conversation. Message-ID is the primary key used by threading algorithms to reconstruct conversations. It is also used during deduplication: when merging two MBOX files that may overlap — for example, two Google Takeout exports from different dates — comparing Message-IDs allows the application to identify and skip messages that already exist in the target archive. In rare cases, Message-IDs may be missing (from very old messages) or duplicated (from buggy sending software). A robust archive tool handles these edge cases by falling back to heuristic matching on other headers such as Date, From, and Subject when a Message-ID is absent or unreliable. ## Related terms [ In-Reply-To / References Email headers (In-Reply-To and References) that link a reply to the message it responds to, enabling mail clients and archive tools to group related messages into conversation threads. ](https://mboxviewerpro.com/glossary/in-reply-to/)[ Deduplication The process of detecting and removing duplicate email messages from an archive, typically by comparing Message-ID values, to avoid redundancy when merging multiple MBOX files. ](https://mboxviewerpro.com/glossary/deduplication/)[ Threading (JWZ) The process of grouping related email messages into conversations by following In-Reply-To and References header links, typically using the JWZ algorithm that supports up to four levels of nesting. ](https://mboxviewerpro.com/glossary/threading/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) MIME # MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. MIME (Multipurpose Internet Mail Extensions, RFC 2045–2049) extends the basic RFC 5322 message format to support content beyond 7-bit ASCII text. Before MIME, email was limited to plain text in English; MIME introduced a system of Content-Type headers and encoding schemes that allow a single message to carry formatted HTML, images, PDF attachments, and text in any language. The core mechanism is the Content-Type header, which declares the media type of a message part — for example, text/plain, text/html, image/jpeg, or application/pdf. A multipart message uses a boundary string to separate its parts, each with its own Content-Type and Content-Transfer-Encoding. Binary content is encoded with Base64 or quoted-printable so it can travel safely through text-based mail infrastructure. Correctly parsing MIME is essential for any email reader. Mbox Viewer implements a MIME decoder that handles nested multipart messages, multiple encodings, charset declarations, and inline images. This decoding runs as part of the streaming parser so that even very large MBOX files are processed efficiently. ## Related terms [ Multipart A MIME message structure that combines multiple content parts — such as plain text, HTML, and attachments — in a single message, each separated by a unique boundary string. ](https://mboxviewerpro.com/glossary/multipart/)[ Charset The character encoding that specifies how bytes in a text part are mapped to readable characters. Common charsets include UTF-8, ISO-8859-1, and Shift\_JIS; a mismatch causes garbled text known as mojibake. ](https://mboxviewerpro.com/glossary/charset/)[ Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. ](https://mboxviewerpro.com/glossary/attachment/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) MSG # MSG Microsoft Outlook's proprietary binary format for a single email message, storing headers, body, and attachments in a Compound Document Structure. Unlike EML, MSG is not a plain-text standard. MSG is a binary file format developed by Microsoft and used by Outlook on Windows. It is based on the Compound Document Structure (OLE2), the same container technology used by legacy Office documents. A single MSG file encapsulates all parts of a message: headers, plain-text and HTML body, embedded images, and attachments — but in a proprietary binary layout rather than MIME text. Because MSG is not an open standard, reading MSG files requires either Outlook itself or a library that reverse-engineers the format. This limits portability: MSG files do not open natively in Thunderbird, Apple Mail, or most Unix mail tools without conversion. Exporting Outlook mail to EML or MBOX before archiving gives better long-term accessibility. Users migrating away from Windows or Outlook often convert MSG files to EML or MBOX as a first step. Once converted, the messages can be opened in cross-platform tools and searched without needing Microsoft software installed. ## Related terms [ EML A single-message file in MIME format, containing headers, body, and attachments. EML files are widely supported across email clients and are useful for archiving or sharing individual messages. ](https://mboxviewerpro.com/glossary/eml/)[ PST Personal Storage Table — Microsoft Outlook's container file for an entire mailbox, including folders, messages, contacts, and calendar items. Also known as OST when used for offline sync with Exchange or Microsoft 365. ](https://mboxviewerpro.com/glossary/pst/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Multipart # Multipart boundary A MIME message structure that combines multiple content parts — such as plain text, HTML, and attachments — in a single message, each separated by a unique boundary string. A multipart MIME message has a Content-Type of multipart/mixed, multipart/alternative, multipart/related, or another multipart subtype. The header specifies a boundary parameter — a unique string like "----=\_Part\_12345" — that appears as a delimiter between each part in the message body. Each part has its own mini-header section declaring its Content-Type, encoding, and optional filename. The most common multipart structure for a formatted email with attachments is nested: the outer container is multipart/mixed, which holds a multipart/alternative part (containing both plain-text and HTML versions of the body) alongside one or more attachment parts. Clients choose which alternative to display based on what they support, and they offer attachments for download. Parsing nested multipart structures correctly is one of the more complex aspects of email processing. Malformed boundary strings, missing headers, or unusual nesting can trip up simpler parsers. A robust MIME implementation must handle edge cases gracefully so that messages with non-standard structure still render usefully rather than appearing as raw text. ## Related terms [ MIME Multipurpose Internet Mail Extensions — the standard that defines how email messages encode non-ASCII text, HTML bodies, attachments, and other binary content within the plain-text structure of email. ](https://mboxviewerpro.com/glossary/mime/)[ Attachment A file — such as a PDF, image, or spreadsheet — embedded in an email message and encoded as a MIME part, separate from the message body, intended for the recipient to save or open. ](https://mboxviewerpro.com/glossary/attachment/)[ Inline image An image embedded directly into an HTML email body using a Content-ID (cid:) reference, rather than attached as a separate downloadable file. The image data is stored as a MIME part within the same message. ](https://mboxviewerpro.com/glossary/inline-image/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) OLM # OLM The archive format Outlook for Mac exports to — a proprietary container that is not the same thing as Windows' PST, and that few other programs can read without conversion. OLM is what Outlook for Mac produces when you use its Export command: a single proprietary container holding messages, attachments, contacts and calendar items. Despite serving the same purpose as PST on Windows, it is a different format, and a PST tool will not read an OLM file — a distinction that catches out anyone migrating between the two platforms. Because the format is proprietary and supported almost nowhere outside Outlook for Mac, an OLM archive is a poor long-term home for your mail. If the application stops running on a future macOS, or the licence lapses, the archive becomes hard to read. Converting to an open format while you still have a working Outlook is the cheap insurance. The usual route is to convert the OLM to MBOX or EML, after which any standard reader — Mbox Viewer among them — can open, search and export the messages. Our guide on converting Outlook PST and OLM archives to MBOX walks through the practical options. ## Related terms [ PST Personal Storage Table — Microsoft Outlook's container file for an entire mailbox, including folders, messages, contacts, and calendar items. Also known as OST when used for offline sync with Exchange or Microsoft 365. ](https://mboxviewerpro.com/glossary/pst/)[ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ MSG Microsoft Outlook's proprietary binary format for a single email message, storing headers, body, and attachments in a Compound Document Structure. Unlike EML, MSG is not a plain-text standard. ](https://mboxviewerpro.com/glossary/msg/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) POP3 # POP3 Post Office Protocol 3 — an older email retrieval protocol that downloads messages from a server to a local device, typically removing them from the server afterward. POP3 (Post Office Protocol version 3, RFC 1939) is one of the earliest protocols for retrieving email. A POP3 client connects to the mail server, downloads new messages to the local device, and — by default — deletes them from the server. This download-and-delete model was designed for the era when users had a single device and limited server storage. Because POP3 removes messages from the server, it effectively creates a local archive, but it does so on only one device. If you check your email on a second device using POP3, that device gets a different set of messages. This contrasts sharply with IMAP, which keeps everything on the server and syncs across all devices. Some mail services still offer POP3 access alongside IMAP, and older client configurations may still use it. If you have accumulated a POP3-downloaded archive in an application like Outlook Express or Apple Mail, that archive is likely stored in MBOX or a similar format and can be opened in tools that support those formats. ## Related terms [ IMAP Internet Message Access Protocol — the standard protocol for accessing email stored on a server, keeping messages synchronized across multiple devices without downloading and deleting them. ](https://mboxviewerpro.com/glossary/imap/)[ SMTP Simple Mail Transfer Protocol — the standard protocol used to send and relay email messages between mail servers. It is used for outgoing mail only; reading email requires IMAP or POP3. ](https://mboxviewerpro.com/glossary/smtp/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) PST # PST OST Personal Storage Table — Microsoft Outlook's container file for an entire mailbox, including folders, messages, contacts, and calendar items. Also known as OST when used for offline sync with Exchange or Microsoft 365. A PST (Personal Storage Table) file is a database-like container created and used by Microsoft Outlook on Windows to store email folders, messages, contacts, tasks, and calendar events in a single file. OST (Offline Storage Table) is a closely related format used when Outlook synchronizes with an Exchange or Microsoft 365 server, keeping a local offline copy of the mailbox. PST files can grow very large — Microsoft recommends keeping them under 50 GB for performance reasons, though they can technically hold more. Because PST is a proprietary binary format, extracting data from it without Outlook requires specialized tools. Corruption is also a known risk with very large PST files, which is why many administrators encourage users to archive to more portable formats. Users who want to migrate away from Outlook or Windows typically export their PST to MBOX or EML first, using tools such as the free libpst/readpst utility or third-party converters. Once in MBOX format, the archived mail can be opened in a wider range of applications. ## Related terms [ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/)[ MSG Microsoft Outlook's proprietary binary format for a single email message, storing headers, body, and attachments in a Compound Document Structure. Unlike EML, MSG is not a plain-text standard. ](https://mboxviewerpro.com/glossary/msg/)[ OLM The archive format Outlook for Mac exports to — a proprietary container that is not the same thing as Windows' PST, and that few other programs can read without conversion. ](https://mboxviewerpro.com/glossary/olm/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Quoted-printable # Quoted-printable A MIME transfer encoding that represents text with mostly ASCII characters, escaping non-ASCII bytes as =XX hex sequences. It keeps the majority of the text human-readable in the raw message source. Quoted-printable (QP, defined in RFC 2045 section 6.7) is an encoding designed for text that is mostly ASCII but contains occasional non-ASCII characters such as accented letters or special symbols. Any byte whose value is outside the printable ASCII range is replaced by an equals sign followed by two uppercase hexadecimal digits — for example, the é character (0xE9 in ISO-8859-1) becomes =E9. Lines may not exceed 76 characters, so long lines are broken with a soft line break =\\r\\n. The advantage of quoted-printable over Base64 for text content is readability: an English email with a few accented words encoded in QP is still largely readable as plain text in the raw source, whereas Base64-encoded text is completely opaque. For text with a high proportion of non-ASCII characters (such as Japanese or Arabic), Base64 is more efficient and is typically chosen instead. A mail client must decode quoted-printable content before displaying it. Missing or incorrect decoding produces text with =XX sequences visible in the body, which is a common symptom of a poorly implemented or legacy email reader. Mbox Viewer decodes quoted-printable transparently as part of MIME processing. ## Related terms [ Base64 A binary-to-text encoding scheme that represents arbitrary binary data using only 64 printable ASCII characters, widely used in email to safely transmit attachments and binary content. ](https://mboxviewerpro.com/glossary/base64/)[ Charset The character encoding that specifies how bytes in a text part are mapped to readable characters. Common charsets include UTF-8, ISO-8859-1, and Shift\_JIS; a mismatch causes garbled text known as mojibake. ](https://mboxviewerpro.com/glossary/charset/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Received # Received The header each mail server adds as a message passes through it. Read from the bottom up, the Received lines reconstruct the route a message actually travelled. Every server that handles a message prepends a Received header describing the handover: which host it came from, which host accepted it, over what protocol, with which internal id, and at what time. Because each is added at the top, the oldest line sits at the bottom — so a message's journey reads upwards, from the sender's first server to the one that delivered it into the mailbox. These headers are the closest thing an email has to a paper trail. They reveal how long a message spent at each hop, whether it went through a mailing list or a corporate gateway, and which IP address it entered the internet from. In investigations and disclosure requests they are usually the first thing anyone looks at. They deserve a caveat, though. A server can only vouch for what it did itself: Received lines below the first host you trust may have been fabricated by whoever sent the message. That is why they are read together with the authentication results — SPF, DKIM and DMARC — rather than on their own. Mbox Viewer shows the full set under Full Headers, and mboxShell under its raw view. ## Related terms [ Header The structured metadata block at the beginning of an email message, containing fields like From, To, Subject, Date, and numerous technical fields that describe how the message was composed, routed, and encoded. ](https://mboxviewerpro.com/glossary/header/)[ SMTP Simple Mail Transfer Protocol — the standard protocol used to send and relay email messages between mail servers. It is used for outgoing mail only; reading email requires IMAP or POP3. ](https://mboxviewerpro.com/glossary/smtp/)[ SPF, DKIM and DMARC The three mechanisms that establish whether a message really came from the domain it claims: SPF authorises sending servers, DKIM signs the message cryptographically, and DMARC ties the two to a published policy. ](https://mboxviewerpro.com/glossary/dkim/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Encoded-word (RFC 2047) # Encoded-word (RFC 2047) RFC 2047 An encoding scheme defined in RFC 2047 ("Encoded-Word") that allows non-ASCII characters in email header fields such as Subject and From, by encoding them as =?charset?encoding?text?= tokens. Email headers are required by RFC 5322 to contain only 7-bit ASCII characters. RFC 2047 provides a workaround: non-ASCII text in headers is represented as an "encoded word" in the form =?charset?B?...?= (Base64) or =?charset?Q?...?= (quoted-printable). For example, a Japanese subject line might appear in the raw message as =?ISO-2022-JP?B?...?= and must be decoded before it can be displayed. Without RFC 2047 decoding, subject lines and sender names containing accented characters, CJK characters, Arabic, or any other non-ASCII script appear as raw encoded strings — completely unreadable to the end user. Correct implementation requires detecting encoded-word tokens anywhere they can legally appear in a header value and decoding each one using the specified charset and encoding. Mbox Viewer decodes RFC 2047 encoded words in all header fields when building its message list and search index. This means that searching for a name written in its original script — for example, a Japanese sender name — will match correctly even though the underlying MBOX file stores the name in encoded form. ## Related terms [ Charset The character encoding that specifies how bytes in a text part are mapped to readable characters. Common charsets include UTF-8, ISO-8859-1, and Shift\_JIS; a mismatch causes garbled text known as mojibake. ](https://mboxviewerpro.com/glossary/charset/)[ Header The structured metadata block at the beginning of an email message, containing fields like From, To, Subject, Date, and numerous technical fields that describe how the message was composed, routed, and encoded. ](https://mboxviewerpro.com/glossary/header/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) App Sandbox # App Sandbox App Sandbox is a macOS security feature that restricts an application's access to system resources, files, and network connections, limiting the potential impact if the app or its dependencies have a vulnerability. App Sandbox is a mandatory requirement for apps distributed through the Mac App Store. A sandboxed app runs in a restricted environment: it can only access files the user explicitly opens or selects (via Open dialogs or drag-and-drop), a temporary scratch directory, and a small set of system services. It cannot read arbitrary files from the filesystem, access other applications' data, or make unauthorized network connections. The sandbox model means that even if a malicious MBOX file attempted to exploit a vulnerability in the parser, the damage it could cause is bounded by the sandbox's restrictions. The app cannot exfiltrate other files from the system, cannot write to arbitrary locations, and cannot communicate with external servers without explicit user permission. Mbox Viewer operates entirely within the App Sandbox. It reads only the MBOX and EML files you open, writes only the companion index file in the same location (using sandbox-extended security-scoped bookmarks), and makes no network connections. The combination of sandbox enforcement and the app's local-only, read-only design provides strong privacy guarantees for your email archive. ## Related terms [ Universal Binary A macOS application bundle that contains native compiled code for both Apple Silicon (ARM64) and Intel (x86\_64) architectures, running natively on either processor without emulation. ](https://mboxviewerpro.com/glossary/universal-binary/)[ HTML email An email message whose body is formatted with HTML and CSS, allowing rich typography, layout, colors, and images. Most modern email is HTML, but privacy and security considerations require careful rendering. ](https://mboxviewerpro.com/glossary/html-email/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) SMTP # SMTP Simple Mail Transfer Protocol — the standard protocol used to send and relay email messages between mail servers. It is used for outgoing mail only; reading email requires IMAP or POP3. SMTP (Simple Mail Transfer Protocol, RFC 5321) is the protocol that mail servers and email clients use to transmit outgoing messages. When you click Send in an email client, the client connects to an SMTP server, authenticates, and hands off the message for delivery. The SMTP server then relays the message from server to server until it reaches the recipient's mail server. SMTP handles only the transmission of messages, not their storage or retrieval. Once a message arrives at the destination server, protocols like IMAP or POP3 allow mail clients to read it. This separation of concerns means that SMTP is not involved in reading, archiving, or searching email — those tasks fall to other protocols and formats. SMTP servers add Received headers to messages as they pass through the relay chain. These headers, visible in the raw message source, record the IP addresses and timestamps of each server that handled the message, which can be useful for tracing delivery issues or verifying authenticity. ## Related terms [ IMAP Internet Message Access Protocol — the standard protocol for accessing email stored on a server, keeping messages synchronized across multiple devices without downloading and deleting them. ](https://mboxviewerpro.com/glossary/imap/)[ POP3 Post Office Protocol 3 — an older email retrieval protocol that downloads messages from a server to a local device, typically removing them from the server afterward. ](https://mboxviewerpro.com/glossary/pop3/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Streaming parser # Streaming parser A parsing technique that reads a file incrementally in small chunks rather than loading the entire file into memory at once, enabling tools to open and index very large MBOX files — tens or hundreds of gigabytes — with low memory usage. A streaming parser processes a file as a sequence of bytes or lines, maintaining only a small buffer and the current parsing state at any moment. This contrasts with a buffered approach that reads the entire file into memory before parsing begins. For MBOX files, a streaming parser can identify message boundaries (the "From " separator lines), extract headers, and record byte offsets without ever holding more than one message in memory at a time. The practical benefit is that file size stops being a limitation. A 50 GB MBOX export from a years-long Gmail archive opens in the same way as a 1 MB test file — the parser reads through it sequentially, building a lightweight index of message positions, and then seeks directly to any message when you select it. Memory usage stays roughly constant regardless of archive size. Mbox Viewer's streaming parser is designed for this use case. On the first open of an MBOX file, it streams through the file to build a binary index recording the byte offset and key metadata for each message. On subsequent opens, the index is loaded in under a second, so the parser only needs to re-stream messages you actually open. ## Related terms [ Binary index A compact index file that Mbox Viewer writes alongside an MBOX archive after the first parse, storing message byte offsets and metadata to enable near-instant reopens without re-scanning the entire file. ](https://mboxviewerpro.com/glossary/binary-index/)[ MBOX A plain-text file format that stores multiple email messages concatenated together, each beginning with a "From " separator line. It is the format Google Takeout produces when you export your Gmail archive. ](https://mboxviewerpro.com/glossary/mbox/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Threading (JWZ) # Threading (JWZ) The process of grouping related email messages into conversations by following In-Reply-To and References header links, typically using the JWZ algorithm that supports up to four levels of nesting. Email threading reconstructs the conversation structure of a mailbox from the message graph encoded in headers. The JWZ algorithm, published by Jamie Zawinski in 1997 and widely adopted in mail clients, works in two phases: first, it builds a tree of messages by following Message-ID, In-Reply-To, and References links; second, it prunes and sorts the tree to produce a clean, readable thread view. When explicit header links are missing — common in older messages or after forwarding — threading algorithms fall back to subject matching: messages with the same subject (after stripping Re:, Fwd:, and similar prefixes) are grouped together. This heuristic produces reasonable results for most conversations but can occasionally merge unrelated messages that happen to share a subject. Thread views dramatically improve navigation in large archives. Instead of scanning thousands of individual messages in date order, you can find a thread, collapse it, and move on. Mbox Viewer applies threading when displaying MBOX archives, grouping messages into conversations and indicating nesting depth up to four levels in the message list. ## Related terms [ Message-ID A globally unique identifier assigned to each email message, specified in the Message-ID header. It is used to track messages, build conversation threads, and detect duplicates when merging archives. ](https://mboxviewerpro.com/glossary/message-id/)[ In-Reply-To / References Email headers (In-Reply-To and References) that link a reply to the message it responds to, enabling mail clients and archive tools to group related messages into conversation threads. ](https://mboxviewerpro.com/glossary/in-reply-to/)[ Gmail labels Gmail's tagging system that assigns one or more labels to each message, serving the role that folders play in traditional email clients. A single message can carry multiple labels simultaneously. ](https://mboxviewerpro.com/glossary/gmail-labels/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [Mbox Viewer](https://mboxviewerpro.com/) [Glossary](https://mboxviewerpro.com/glossary/) Universal Binary # Universal Binary A macOS application bundle that contains native compiled code for both Apple Silicon (ARM64) and Intel (x86\_64) architectures, running natively on either processor without emulation. Apple introduced Universal Binary 2 with the transition from Intel processors to Apple Silicon (M-series) chips beginning in 2020. A Universal Binary app bundle contains two compiled versions of the code — one for ARM64 (Apple Silicon) and one for x86\_64 (Intel) — merged into a single download. When the user launches the app, macOS automatically selects the correct binary for the machine's processor. Apps that are not Universal Binaries but include only Intel (x86\_64) code run on Apple Silicon Macs through Rosetta 2, Apple's translation layer. Rosetta 2 is transparent and reasonably fast, but a native ARM64 build offers better performance and lower energy consumption, which matters for processing-intensive tasks like parsing large MBOX files. Mbox Viewer is distributed as a Universal Binary, meaning it runs natively on both Apple Silicon and Intel Macs without requiring Rosetta 2. Users on either architecture get the full native performance of their hardware. ## Related terms [ App Sandbox App Sandbox is a macOS security feature that restricts an application's access to system resources, files, and network connections, limiting the potential impact if the app or its dependencies have a vulnerability. ](https://mboxviewerpro.com/glossary/sandbox/)[ Streaming parser A parsing technique that reads a file incrementally in small chunks rather than loading the entire file into memory at once, enabling tools to open and index very large MBOX files — tens or hundreds of gigabytes — with low memory usage. ](https://mboxviewerpro.com/glossary/streaming-parser/) [Back to the full glossary](https://mboxviewerpro.com/glossary/) ## Read your MBOX files on Mac and Windows [Download on the Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Convert MBOX to CSV, EML, and Text (and Extract Attachments) A practical guide to exporting an MBOX file into CSV spreadsheets, individual EML messages, plain text, and PDF — plus how to extract every attachment in bulk — using Mbox Viewer on Mac. PublishedMay 18, 2026 An [MBOX](https://mboxviewerpro.com/glossary/mbox/) file is a great archive, but sometimes you need your email in a *different* shape: a spreadsheet for analysis, individual `.eml` files for another mail client, plain text for grepping, or just the attachments pulled out into a folder. This guide shows you how to do all of that on a Mac with [Mbox Viewer](https://apps.apple.com/app/mbox-viewer-pro/id6759237715). ## Choosing the right output format Each format serves a different purpose. Pick the one that matches what you’re trying to do. | Format | Best for | What you get | | --- | --- | --- | | **CSV** | Analysis, reporting, audits | One row per email with date, sender, recipient, subject, size | | **EML** | Importing into another mail app | One standalone file per message, headers intact | | **Text** | Search with command-line tools, plain reading | Readable plain-text body of each message | | **PDF** | Sharing, legal, printing | A formatted, fixed snapshot of a message | | **Attachments** | Recovering files | The original files, saved to a folder | ## Convert MBOX to CSV A CSV export turns thousands of emails into a tidy spreadsheet you can open in Numbers or Excel. It’s ideal for spotting who emails you most, auditing a date range, or handing a summary to someone else. 1. Open your `.mbox` file in **Mbox Viewer**. 2. (Optional) **Search or filter** to narrow down to the messages you care about — for example `from:billing@ date:2025`. 3. Select the messages you want (or press **Cmd-A** to select all). 4. Choose **File → Export → CSV**. 5. Pick a destination and save. Each row contains the key metadata fields, so you can sort, pivot, and chart your mail however you like. ## Convert MBOX to EML [EML](https://mboxviewerpro.com/glossary/eml/) is the universal “one message, one file” format. Exporting to EML is the cleanest way to move selected emails into Apple Mail, Outlook, or Thunderbird without dragging the whole archive along. 1. Select one or more messages in Mbox Viewer. 2. Choose **File → Export → EML**. 3. Choose a folder. Mbox Viewer writes one `.eml` file per message, preserving headers, formatting, and attachments. You can then drag those files straight into another mail client. ## Export to text or PDF - **Text:** Select messages and choose **Export → Text** to get clean, readable bodies — perfect for `grep`, indexing, or pasting into a document. - **PDF:** Select a message and choose **Export → PDF** for a formatted, shareable snapshot. This is the go-to format for legal hand-offs and printing, because the layout is fixed. ## Extract attachments in bulk Hunting through hundreds of emails for that one PDF invoice is tedious. Mbox Viewer can pull **every [attachment](https://mboxviewerpro.com/glossary/attachment/)** out at once. 1. Select the messages (or all of them). 2. Choose **File → Export → Attachments**. 3. Pick a destination folder. The app saves each attachment with its original filename, so you end up with a clean folder of documents, images, and files — no email wrapper around them. > **Tip:** Combine search with extraction. Run `has:attachment from:accounting@` first, then export attachments to grab just the invoices. ## A typical workflow Here’s how these pieces fit together for a common task — *archiving a year of project email*: 1. Open the MBOX and search `subject:"Project Atlas" date:2025`. 2. Export the matching messages to **EML** for safekeeping. 3. Export the same set to **CSV** for a quick index. 4. Extract **attachments** into a `Project Atlas/Files` folder. In a few minutes you’ve turned one giant archive into organized, reusable pieces — and nothing ever left your Mac. ## Your email, in any format you need Mbox Viewer makes MBOX a starting point, not a dead end. Convert, export, and extract with a few clicks. [Get Mbox Viewer on the Mac App Store →](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Convert Outlook PST/OLM to MBOX (Mac & Windows) Outlook stores mail in PST (Windows) or OLM (Mac), which Mbox Viewer can't open directly. Here's how to convert PST and OLM files to standard mbox — free, step by step — then read them. PublishedJune 18, 2026 Microsoft Outlook doesn’t use [mbox](https://mboxviewerpro.com/glossary/mbox/). On Windows it stores everything in a [**PST**](https://mboxviewerpro.com/glossary/pst/) database; Outlook for Mac uses an **OLM** archive. Neither is mbox, so Mbox Viewer can’t open them directly — you convert to standard mbox first, then open the result. This guide covers a free, reliable route for both formats and works on **Mac and Windows**. ## Why convert at all? PST and OLM are proprietary, single-vendor containers. Converting to the open mbox format frees your mail from Outlook, gives you one portable archive, and lets you read, [search](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/) and export it in Mbox Viewer without an Outlook licence or a running mail account. ## Convert a PST file (Outlook for Windows) The cleanest free method uses **Mozilla Thunderbird** as a bridge — no paid converter required: 1. Install [Thunderbird](https://www.thunderbird.net/) and the free [ImportExportTools NG](https://addons.thunderbird.net/thunderbird/addon/importexporttools-ng/) add-on. 2. In Outlook, make sure the mail you want is in a `.pst` (in Outlook: **File → Open & Export → Import/Export → Export to a file → Outlook Data File (.pst)**). 3. In Thunderbird, install the **ImportExportTools NG** add-on, then use its tools (or the Thunderbird import wizard) to bring the PST data into a Local Folder. 4. Right-click the folder → **ImportExportTools NG → Export folder** to write a standard `.mbox` file. Prefer a one-step tool? Dedicated **PST-to-MBOX converters** exist for Windows; pick a reputable one, and always work on a *copy* of your PST. ## Convert an OLM file (Outlook for Mac) OLM is Mac-only and a bit more involved: 1. In Outlook for Mac, export with **Tools → Export…** to create the `.olm` (work on a copy). 2. Use an **OLM-to-MBOX converter**, or re-import the OLM into a mail client that can then export mbox (Thunderbird with ImportExportTools NG, as above). 3. The output is one or more `.mbox` files. ## Open the result in Mbox Viewer Once you have a `.mbox` file (or an extension-less mbox), open it with **Mbox Viewer**: - **Mac:** double-click, drag & drop, or **File → Open**. - **Windows:** double-click in File Explorer, drag onto the window, or **File → Open**. (Mbox Viewer for Windows is available on the [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB).) You get instant browsing, full [search syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), threaded conversations, [attachment](https://mboxviewerpro.com/glossary/attachment/) previews and export to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or plain text — even for multi-gigabyte mailboxes, thanks to the [streaming parser](https://mboxviewerpro.com/glossary/streaming-parser/). Everything is **local and read-only**: your converted archive is never modified. ## Related guides - [How to open an MBOX file on Mac](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/) - [How to open an MBOX file on Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/) - [Convert MBOX to CSV, EML and attachments](https://mboxviewerpro.com/guides/convert-mbox-to-csv-and-eml/) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Export Gmail with Google Takeout (and Open It on Mac) A step-by-step guide to exporting your Gmail to an MBOX file with Google Takeout, downloading it safely, and opening it instantly in Mbox Viewer on macOS. PublishedMay 12, 2026 Gmail is fast and convenient, but your email doesn’t really belong to you until you have a copy you control. [**Google Takeout**](https://mboxviewerpro.com/glossary/google-takeout/) is the official way to download everything in your mailbox as a single, portable [**MBOX**](https://mboxviewerpro.com/glossary/mbox/) file. This guide walks you through the whole process — from requesting the archive to opening it on your Mac with [Mbox Viewer](https://apps.apple.com/app/mbox-viewer-pro/id6759237715). ## What is Google Takeout? Google Takeout is a free Google service that lets you export your data from Gmail, Drive, Photos, and dozens of other products. For email, it produces a standard **MBOX** file: one plain-text container that holds every message, header, and attachment in your account. Because MBOX is an open format, you can keep that file forever and open it on any computer — even decades from now. ## Step 1: Request your Gmail export 1. Go to [takeout.google.com](https://takeout.google.com) and sign in with the account you want to back up. 2. Click **Deselect all** so you only export what you need. 3. Scroll down, find **Mail**, and tick its checkbox. 4. (Optional) Click **All Mail data included** to choose specific [labels](https://mboxviewerpro.com/glossary/gmail-labels/) instead of your entire mailbox — useful if you only want, say, *Work* or *Invoices*. 5. Click **Next step** at the bottom. ## Step 2: Choose delivery and format On the next screen you’ll set how the archive is delivered: | Option | Recommended setting | Why | | --- | --- | --- | | Delivery method | Send download link via email | Simplest for a one-time backup | | Frequency | Export once | Choose scheduled exports only for recurring backups | | File type | `.zip` | Opens natively on macOS | | File size | 50 GB | Fewer files to download and reassemble | Click **Create export**. Google now builds your archive in the background. ## Step 3: Wait for the email Exports are not instant. A small mailbox may be ready in minutes; a large one with years of history can take **several hours, or even a day or two**. Google will email you a download link when it’s finished. The link stays valid for about a week, so download it promptly. ## Step 4: Download and unzip 1. Open the email from Google and click **Download your files**. 2. Sign in again to confirm it’s really you. 3. Save the `.zip` to your **Downloads** folder. 4. Double-click the `.zip` in Finder to extract it. Inside, look in `Takeout/Mail/`. You’ll find one or more files ending in **`.mbox`** — for example `All mail Including Spam and Trash.mbox`. This single file can be many gigabytes if you’ve used Gmail for years. ## Step 5: Open the MBOX in Mbox Viewer This is where most people get stuck. Apple Mail can *import* MBOX, but it copies every message into your live mailbox — slow, messy, and risky for huge files. **Mbox Viewer** takes a different approach: it opens the file directly, without importing anything. 1. Open **Mbox Viewer** on your Mac. 2. Drag the `.mbox` file onto the window, or choose **File → Open**. 3. The app streams the file and shows your messages in seconds — even for archives of **10 GB or more**. From there you can: - **Search** across every message with operators like `from:`, `subject:`, and `has:attachment`. - **Read** full messages with formatting and inline images intact. - **Export** selected emails to [EML](https://mboxviewerpro.com/glossary/eml/), PDF, CSV, or plain text. - **Extract attachments** in bulk to a folder. Because Mbox Viewer reads the file in place and never phones home, your email stays entirely on your Mac. ## Tips for large mailboxes - If Takeout splits your export into multiple numbered MBOX files, you can open each one separately in Mbox Viewer. - Store the archive on an external drive or in a backup so you always have an offline copy. - Run Takeout once or twice a year to keep your local archive current. ## Ready to open your Gmail archive? You’ve done the hard part — your mail is now a file you own. Open it the fast, private way. [Get Mbox Viewer on the Mac App Store →](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Open an Apple Mail Export (.mbox Folder) on Mac Apple Mail exports a .mbox folder with a file named “mbox” inside — that file is your mail in standard mbox format. Here's how to export from Mail and read the result with Mbox Viewer. PublishedJune 11, 2026 Apple Mail (the built-in Mail app on macOS) can export any mailbox to the open [**mbox**](https://mboxviewerpro.com/glossary/mbox/) format. It’s the perfect way to archive old mail, hand a mailbox to someone else, or keep a copy outside of Mail. The export has one quirk worth knowing about — but Mbox Viewer handles it for you. Let’s walk through it. ## Step 1: export the mailbox from Apple Mail 1. Open **Mail** and select the mailbox you want to export in the sidebar. 2. Choose **Mailbox → Export Mailbox…** from the menu bar. 3. Pick a destination folder and click **Choose**. Mail writes the export to the folder you picked. ## Step 2: understand what Mail actually exported Here’s the quirk: Apple Mail doesn’t export a single file. It creates a **folder** named after your mailbox, ending in `.mbox` — for example `Inbox.mbox` or `Receipts 2019.mbox`. Inside that folder you’ll find: - a file named simply **`mbox`** — this is the real archive, with every message in standard mbox format - one or more `.plist` files — metadata that Mail uses internally; you can ignore them So `Inbox.mbox` is a container; the file called `mbox` inside it is your mail. ## Step 3: open the export with Mbox Viewer Mbox Viewer opens the `.mbox` export package directly — you don’t need to dig out the inner file: 1. In Finder, locate the exported folder (e.g. `Inbox.mbox`). 2. **Drag it onto Mbox Viewer** (or use **File → Open** in Mbox Viewer and select the `.mbox` folder). Mbox Viewer finds the `mbox` data file inside the package automatically and opens it. (Opening the inner `mbox` file directly still works too, if you prefer.) That’s it. It opens read-only, your original export is never modified, and you can [search](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), browse threads, preview [attachments](https://mboxviewerpro.com/glossary/attachment/) and export individual messages to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or text. ## Nested mailboxes If you export a mailbox that contains sub-mailboxes, Mail creates nested `.mbox` folders. Each level has its own inner `mbox` file — open each one the same way. ## Why this beats re-importing into Mail Re-importing an archive into Apple Mail mixes it back into your live mail and can take a long time for big exports. Opening the export with Mbox Viewer keeps the archive exactly as it is — a self-contained, read-only snapshot you can search instantly, even when it’s [tens of gigabytes](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-mac/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Open an Apple Mail Export (.mbox) on Windows Moving from Mac to PC? Apple Mail exports a .mbox package that looks like a folder on Windows. Here's how to find the real mailbox inside it and read it with Mbox Viewer. PublishedJune 18, 2026 Switching from a Mac to a Windows PC and carrying your old Apple Mail archive with you? When Apple Mail does **Mailbox → Export Mailbox**, it produces something called `MyMailbox.mbox` — but it isn’t a single file. On macOS it’s a **package** (a special folder), and once it lands on Windows it shows up as an **ordinary folder**, which is why double-clicking it just opens a directory. This guide shows you what’s inside and how to read it on Windows. > Mbox Viewer for Windows is available on the [**Microsoft Store**](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB); the steps below show how to use it. ## Why the “.mbox” looks like a folder on Windows macOS packages are folders that the Mac presents as one item. Windows has no concept of packages, so when you copy an Apple Mail `.mbox` to a PC (via USB drive, network share or cloud), File Explorer shows a folder named `MyMailbox.mbox` containing a few items: ``` MyMailbox.mbox\ ├─ mbox ← the actual mail, standard mbox format, no extension ├─ Info.plist └─ (a table_of_contents / index file) ``` The file simply named **`mbox`** (no extension) is your real mailbox in standard [mbox](https://mboxviewerpro.com/glossary/mbox/) format. The other files are Apple’s metadata and can be ignored. ## Step 1: bring the export over to your PC Copy the **whole** `.mbox` folder from the Mac to the PC — don’t cherry-pick. Keep the inner `mbox` file intact; it’s the only piece that matters but it must arrive uncorrupted. ## Step 2: open it with Mbox Viewer 1. Install **Mbox Viewer** from the Microsoft Store. 2. In Mbox Viewer choose **File → Open** and navigate *into* the `MyMailbox.mbox` folder. 3. Select the inner file named **`mbox`** and open it. No need to rename it or add an extension — Mbox Viewer reads extension-less mbox files directly. If you exported several mailboxes, repeat for each `.mbox` folder. Nested mailboxes from Apple Mail appear as nested folders, each with its own inner `mbox` file. ## What you get Your mail opens in seconds — [search](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), threaded conversations, [attachment](https://mboxviewerpro.com/glossary/attachment/) previews and export to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or plain text — all **local and read-only**, so the migrated archive is never altered. New to mbox on Windows? See [how to open an MBOX file on Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/). Coming from Outlook instead of Apple Mail? See [how to convert PST/OLM to mbox](https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Open a Gmail (Google Takeout) MBOX File on Windows Downloaded your Gmail with Google Takeout and got a giant .mbox inside a ZIP? Here's how to unzip it on Windows and open the mailbox with Mbox Viewer — no import, no Gmail login. PublishedJune 18, 2026 [**Google Takeout**](https://mboxviewerpro.com/glossary/google-takeout/) is the official way to download a full copy of your Gmail, and it hands you your mail as a single [**mbox**](https://mboxviewerpro.com/glossary/mbox/) file inside one or more ZIP archives. On Windows the awkward part isn’t the email — it’s getting a multi-gigabyte file *out* of the ZIP and finding something that can actually read it. Here’s the clean path. If you still need to *create* the export, follow [how to export Gmail with Google Takeout](https://mboxviewerpro.com/guides/how-to-export-gmail-with-google-takeout/) first. > Mbox Viewer for Windows is available on the [**Microsoft Store**](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB); the steps below show how to use it. ## Step 1: unzip the Takeout download properly Takeout gives you files like `takeout-20260618T....zip`. Large mailboxes are split across several ZIPs (`-001`, `-002`, …). 1. Put **all** the ZIP parts in the same folder. 2. Right-click the first one → **Extract All…** and pick a destination with plenty of free space (a 15 GB mailbox needs ~15 GB extracted). 3. Don’t try to read the `.mbox` *inside* the ZIP preview — Windows can’t stream it from there, and copying out one file at a time misses the split parts. Always extract fully first. For very large archives, the built-in extractor can be slow; [7-Zip](https://www.7-zip.org/) is a faster, free alternative. ## Step 2: find the .mbox file After extracting, browse to: ``` Takeout\Mail\ ``` You’ll find files such as `All mail Including Spam and Trash.mbox` (and one per label if you chose specific labels). That `.mbox` is your entire mailbox — often several gigabytes. ## Step 3: open it with Mbox Viewer Windows has no built-in mbox reader and Outlook can’t open it, so use Mbox Viewer: 1. Install **Mbox Viewer** from the Microsoft Store. 2. **Double-click** the `.mbox`, or drag it onto the window, or use **File → Open**. 3. The whole mailbox loads in seconds via the [streaming parser](https://mboxviewerpro.com/glossary/streaming-parser/) — no Gmail login, no internet, no import. ## Make sense of a Gmail archive Gmail exports carry [**labels**](https://mboxviewerpro.com/glossary/gmail-labels/) instead of folders, and a message can have several. Mbox Viewer reads those labels straight from the Takeout file and lets you browse by label in the sidebar, [search with full query syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/) and export anything to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or plain text. Everything stays **local and read-only** — your backup is never modified and nothing is uploaded. ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Open an MBOX File on Mac (Even Huge Ones) Three ways to open an MBOX file on macOS — Apple Mail, Thunderbird or a dedicated viewer — with the steps for each, and which one to pick for a multi-gigabyte Gmail archive. UpdatedAugust 29, 2026 **There are three ways to open an MBOX file on a Mac.** You can import it into **Apple Mail**, which is free and already installed but copies every message into your live mailbox. You can use **Thunderbird**, which needs an add-on to take a loose file. Or you can open it with a **dedicated viewer**, which reads the file where it sits and changes nothing. Which one fits depends on how big the file is and whether you want that mail mixed into your inbox. The three methods are below, with the steps for each. ## What is an MBOX file? [**MBOX**](https://mboxviewerpro.com/glossary/mbox/) is a long-standing, open standard for storing email. Instead of one file per message, an MBOX file concatenates *every* message — [headers](https://mboxviewerpro.com/glossary/header/), body, and [attachments](https://mboxviewerpro.com/glossary/attachment/) — into a single plain-text container. Each email begins with a line starting with `From` and runs until the next one. You’ll most often encounter MBOX files from: - [**Google Takeout**](https://mboxviewerpro.com/glossary/google-takeout/) exports of Gmail - **Apple Mail** and **Thunderbird** mailbox exports - Migrations away from Outlook, Yahoo, or hosted email - Archived mailboxes handed over by IT during e-discovery Because the format is open and text-based, an MBOX file is the perfect long-term archive: no proprietary database, no vendor lock-in. What it isn’t is convenient — macOS has no built-in way to just *look inside* one. Double-clicking a `.mbox` file does nothing useful, because nothing is registered to handle that extension. ## Option 1 — Import it into Apple Mail Apple Mail is already on your Mac and it reads mbox natively. According to [Apple’s own documentation](https://support.apple.com/guide/mail/import-or-export-mailboxes-mlhlp1030/mac): 1. Open **Mail**. 2. Choose **File → Import Mailboxes**. 3. Select **Files in mbox format**. 4. Locate the folder that contains your mail files and click **Continue**. Your messages land in a new mailbox called **Import** in the Mail sidebar. From there you can drag them into other mailboxes and delete the Import mailbox afterwards. **When this is the right choice:** the archive is small, and you actually want those messages back in your day-to-day mail — searchable alongside everything else, synced to your other devices if the mailbox lives on a server. **When it isn’t:** importing *copies* every message into your live mail store. A 10 GB Takeout export becomes 10 GB inside Mail, the import can run for a very long time, and undoing it means deleting the imported mailbox by hand. If you only want to *read* an old archive — to find one message, or check what’s in a backup — you’re rebuilding your mailbox to answer a question. ## Option 2 — Open it in Thunderbird Thunderbird stores its own mail in mbox format, so it understands the file perfectly well. The catch is that it has no menu command for opening a loose `.mbox` file: the usual route is the **ImportExportTools NG** add-on, which adds an import option for mbox files and directories. **When this is the right choice:** you already use Thunderbird, or you want the archive in a mail client that isn’t Apple Mail. **When it isn’t:** installing a full email client plus an add-on is a lot of moving parts just to read a file. Thunderbird also has to index what you import, which is slow on very large archives. ## Option 3 — Open it directly with a viewer A dedicated viewer skips the import entirely: it opens the MBOX file where it already is and shows you the messages. Nothing is copied, nothing is merged into your mail, and the original file is left exactly as it was. [Mbox Viewer](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) is a native macOS app built for this. To open a file: 1. Launch **Mbox Viewer**. 2. Drag your `.mbox` file onto the window (or use **File → Open**). 3. Your messages appear in a three-pane layout within seconds. No setup, no account, no waiting for an import to finish. It reads [EML](https://mboxviewerpro.com/glossary/eml/) files too. ### Why it handles huge archives It’s built around [**streaming**](https://mboxviewerpro.com/glossary/streaming-parser/). Rather than loading a multi-gigabyte file into memory, it builds a [binary index](https://mboxviewerpro.com/glossary/binary-index/) and reads only the messages you actually open. In practice that means a 50 GB archive opens in under five minutes, reopens in under a second once the index exists, and stays below 600 MB of RAM while you browse. It’s a native Apple-silicon binary, so there’s no Electron or Java runtime in the way, and **your email never leaves your Mac** — no cloud, no account, no telemetry. Remote images are blocked by default, so opening an old archive doesn’t quietly tell senders you read their mail. The free version opens mailboxes up to 1 GB, which covers most single exports. Larger files need the Pro unlock, a one-time in-app purchase with no subscription. ## Which one should you use? | | Apple Mail | Thunderbird | Mbox Viewer | | --- | --- | --- | --- | | Already installed | Yes | No | No | | Copies mail into your mailbox | Yes | Yes | No | | Changes the original file | No | No | No, read-only | | Comfortable with 10 GB+ | No | Not really | Yes | | Extra software needed | None | Client + add-on | The app | | Free | Yes | Yes | Up to 1 GB | Put simply: **import it into Apple Mail if you want the mail back in daily use, and use a viewer if you want to read an archive without touching your mailbox.** For anything measured in gigabytes, the viewer is the only one of the three that stays comfortable. ## What if your .mbox is a folder? If Apple Mail produced the file, you may find that `.mbox` isn’t a file at all — it’s a package that *looks* like a folder, with a file literally named `mbox` inside it. That inner file is standard MBOX, and it’s what the methods above are looking for. It’s a common source of confusion, and we cover it in detail in [opening an Apple Mail export on a Mac](https://mboxviewerpro.com/guides/how-to-open-apple-mail-export-on-mac/). ## Frequently asked questions **How do I read an MBOX file on a Mac without importing it?** Use a dedicated viewer. Apple Mail and Thunderbird both work by importing — that is, copying — the messages into their own store. A viewer reads the file in place and leaves it alone. **Can I open a .mbox file on a Mac without installing anything?** Yes, with Apple Mail: **File → Import Mailboxes → Files in mbox format**. It’s free and built in. The trade-off is that it copies everything into your mailbox. **How do I open a very large MBOX file, 10 GB or more?** Not by importing it. At that size Apple Mail imports take a long time and duplicate the whole archive inside your mail store. A streaming viewer opens the file without loading it into memory. **Will opening it modify my original file?** Not with a read-only viewer — Mbox Viewer never writes to your archive. Importing doesn’t modify the source file either, but it does create a full second copy inside your mail client. **Can I open several MBOX files at once?** Yes — open each one in its own window and switch between them. **Does it work offline?** Completely. There’s no sign-in and no network requirement. ## Open your MBOX the easy way If you want that archive back in your daily mail, Apple Mail does the job for free. If you just want to read it — or it’s measured in gigabytes — open it where it sits. [Get Mbox Viewer on the Mac App Store →](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Open an MBOX File on Windows 10 and 11 Three ways to open and read an MBOX file on Windows: import it into Thunderbird, open it with a dedicated viewer, or take a quick look. Steps for each, and which one fits your file. PublishedJune 18, 2026 **There are three ways to open an MBOX file on Windows, and none of them is Outlook.** You can import it into **Thunderbird**, which is free but copies every message onto your disk a second time. You can open it with a **dedicated viewer**, which reads the file where it sits and copies nothing. Or, if the file is small and you only want to see what’s inside, you can take a quick look without installing an email client at all. Which fits depends on the size of the file, how private the mail is, and whether you need it once or every week. ## What an MBOX file is, and why Windows can’t open it [**MBOX**](https://mboxviewerpro.com/glossary/mbox/) is an open, decades-old standard for storing email. Instead of one file per message, it concatenates *every* message — [headers](https://mboxviewerpro.com/glossary/header/), body and [attachments](https://mboxviewerpro.com/glossary/attachment/) — into a single plain-text container. On a PC you’ll typically meet `.mbox` files from [**Google Takeout**](https://mboxviewerpro.com/glossary/google-takeout/) exports of Gmail, Thunderbird mailboxes copied off another machine, migrations away from Outlook or Yahoo, and mailboxes handed over by IT during e-discovery. Windows ships nothing that reads it, so double-clicking a `.mbox` file gets you nowhere: File Explorer either asks which app to use or hands the file to something that chokes. Two dead ends are worth naming, because most people try them first. **Outlook cannot open an MBOX file.** It keeps mail in its own [PST](https://mboxviewerpro.com/glossary/pst/) database and has never shipped an mbox importer — not 2016, not 2021, not Microsoft 365, not the new Outlook for Windows. **Notepad chokes on it.** Opening the file in Notepad or Word “works” only for tiny files. A real archive is hundreds of megabytes to tens of gigabytes of raw text, and a text editor loads all of it into memory at once. ## Option 1 — Import the MBOX into Thunderbird (free) Thunderbird is free, runs on Windows 10 and 11, and stores its own mail in mbox format, so it understands the file perfectly well. The catch: it has no menu command for opening a loose `.mbox` file. The usual route is the free **ImportExportTools NG** add-on: 1. Install **Thunderbird** and launch it. Skip the account setup: you don’t need a mail account to read an archive. 2. Install [**ImportExportTools NG**](https://addons.thunderbird.net/thunderbird/addon/importexporttools-ng/) from the Add-ons Manager. 3. In the sidebar, right-click a folder under **Local Folders**, open the add-on’s submenu and choose the option to import an mbox file. 4. Pick your `.mbox` file. The messages appear as a new folder, readable and searchable like any other. **What it costs you.** Thunderbird *copies* every message into its profile folder under `%APPDATA%\Thunderbird`: a 12 GB archive becomes another 12 GB on disk, on top of the original, and the import plus indexing runs for a very long time on a mailbox of tens of gigabytes. It works the other way round too: because Thunderbird stores mail in mbox, the files inside its own profile *are* MBOX files, openable with anything that reads the format. See [how to open a Thunderbird mbox on Windows](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-windows/). **When this is the right choice:** the archive is moderate in size, you have the disk space, and you want that mail back in a client where you can reply to it. ## Option 2 — Open the MBOX file with a dedicated viewer A viewer skips the import: it opens the file where it already is and leaves the original exactly as it was. [Mbox Viewer](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) is a native Windows app built for that — no bundled browser, no Java runtime: 1. Install **Mbox Viewer** from the Microsoft Store. 2. Open your `.mbox` file one of three ways: - **Double-click** it in File Explorer (Mbox Viewer registers the `.mbox` type), or - **Drag** the file from File Explorer onto the Mbox Viewer window, or - Use **File → Open** and browse to it. 3. The message list appears in seconds — browse, [search with full query syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), read threaded conversations, preview attachments. ### Why it copes with files of any size It’s built around a [**streaming parser**](https://mboxviewerpro.com/glossary/streaming-parser/). Rather than loading a multi-gigabyte file into memory, it builds a [binary index](https://mboxviewerpro.com/glossary/binary-index/) beside the file and reads only the messages you open. A 50 GB archive opens in under five minutes the first time, reopens in under a second afterwards, and stays below 600 MB of RAM. It is strictly **read-only** and blocks remote images by default. You can export to [EML](https://mboxviewerpro.com/glossary/eml/), CSV, text or a new mbox — see [converting mbox to CSV and EML](https://mboxviewerpro.com/guides/convert-mbox-to-csv-and-eml/). The free version opens mailboxes up to 1 GB; larger files need the Pro unlock, a one-time in-app purchase with no subscription and no account. **When this is the right choice:** the file is large, you only want to read it, or you don’t want an old archive mixed into your everyday mailbox. ## Option 3 — You only want a quick look inside If the file is a few megabytes and the question is simply *what is in here*, you don’t need an email client. A capable text editor shows the raw contents — **not Notepad**, which hangs or truncates, but something like Notepad++ or a code editor, which handle a few hundred megabytes without complaint. Headers appear plainly; message bodies are often base64 gibberish. Enough to confirm which mailbox you’re holding and roughly what dates it spans, not a way to read the mail. There’s also the [free online MBOX viewer](https://mboxviewerpro.com/online-viewer/), which opens in a browser with nothing to install. It processes the file in the browser rather than uploading it, but it is still a website rather than software on your own machine, and the tab has to hold the archive in memory. For a confidential mailbox, or anything measured in gigabytes, stay local. ## Which option should you choose? | | Thunderbird | Mbox Viewer | Text editor | | --- | --- | --- | --- | | Extra software | Client + add-on | The app | Usually none | | Copies mail to disk | Yes | No | No | | Changes the original | No | No, read-only | Only if you save | | Fine at 10 GB and up | Not really | Yes | No | | Free | Yes | Up to 1 GB | Yes | In short: if the archive is under a gigabyte and you want that mail back in daily use, **Thunderbird** does the job for nothing. If you only need to *read* it — find one message, check a backup, work through a mailbox handed to you for e-discovery — a **viewer** fits better: nothing is copied, the original is untouched, and past a few gigabytes it’s the only one of the three that stays comfortable. For a one-off peek at a small file, a text editor answers the question in a minute. ## Files without a `.mbox` extension Some mailboxes — notably [Thunderbird](https://mboxviewerpro.com/guides/how-to-open-thunderbird-mbox-on-windows/) ones named `Inbox` or `Sent` — are mbox files with **no extension at all**. Mbox Viewer opens them through **File → Open**; there’s no need to rename them to `.mbox` first. ## Frequently asked questions ### Can Outlook open an MBOX file? No. Outlook stores mail in its own PST database and has no mbox importer, so there is nothing to point at your file. If you really need those messages inside Outlook, export them from a viewer as individual [EML](https://mboxviewerpro.com/glossary/eml/) files — Outlook opens `.eml` one at a time. The other direction is covered in [converting PST and OLM to mbox](https://mboxviewerpro.com/guides/convert-outlook-pst-olm-to-mbox/). ### How do I read an MBOX file in Windows 11? Exactly as in Windows 10: nothing about the format changed between them, and neither version registers `.mbox`. Use one of the three options above; once an app claims the file type, double-clicking in File Explorer opens it straight away. ### Is there a way to view an MBOX file without installing anything? Yes, within limits. The [online viewer](https://mboxviewerpro.com/online-viewer/) runs in your browser, and a text editor you already have shows the raw file. Both are fine for small archives. Anything sizeable, or anything you want to search properly, needs an app on the machine. ### Will opening the file modify my original MBOX? It depends what you open it with. A read-only viewer never writes to your archive. Thunderbird doesn’t modify the source either, but it does create a full second copy inside its profile. A text editor is the one real risk: an accidental save can corrupt the file. ### How do I open a very large MBOX file, 10 GB or more? Not by importing it. At that size an import means doubling the archive on disk and a long indexing pass. A streaming viewer opens the file without loading it into memory, which is what makes tens of gigabytes practical on an ordinary PC. ## Your data stays on your PC Everything above happens locally: no cloud, no telemetry, and it all works offline, so no email leaves your computer. If your archive came out of Google, [how to open a Gmail Takeout mbox on Windows](https://mboxviewerpro.com/guides/how-to-open-gmail-takeout-mbox-on-windows/) picks up from here. [Get Mbox Viewer on the Microsoft Store →](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Open a Thunderbird MBOX File on Mac Thunderbird stores your mail in standard mbox files — they just have no extension. Here are two easy ways to read them on macOS with Mbox Viewer, without importing anything. PublishedJune 11, 2026 Mozilla Thunderbird has been storing email in the open [**mbox**](https://mboxviewerpro.com/glossary/mbox/) format for more than two decades. That’s great news: it means your Thunderbird mail is *already* in a format any standard mbox reader can open — including Mbox Viewer on your Mac. The only catch is that Thunderbird’s mailbox files have **no file extension**, so they don’t look openable at first glance — but Mbox Viewer opens them directly anyway. This guide shows the two ways to get there. ## Where Thunderbird keeps your mail Each mailbox (Inbox, Sent, Archives, your custom folders…) lives as one mbox file inside your Thunderbird profile: - **macOS:** `~/Library/Thunderbird/Profiles//Mail/Local Folders/` - **Windows:** `%APPDATA%\Thunderbird\Profiles\\Mail\Local Folders\` - **Linux:** `~/.thunderbird//Mail/Local Folders/` Inside you’ll find files named `INBOX`, `Sent`, `Archives` and so on — **without any extension** — next to `.msf` files of the same name. The `.msf` files are just Thunderbird’s index; you can ignore them. The extension-less files are your actual mail, in standard mbox format. ## Option 1: export with ImportExportTools NG (recommended) The free [ImportExportTools NG](https://addons.thunderbird.net/thunderbird/addon/importexporttools-ng/) add-on is the cleanest route: 1. In Thunderbird, install **ImportExportTools NG** from the Add-ons manager. 2. Right-click any folder → **ImportExportTools NG → Export folder**. 3. Pick a destination. You get a proper `.mbox` file. 4. Open that file with **Mbox Viewer** — double-click or drag & drop. This works for one folder or your whole account, and the export already carries the `.mbox` extension, so it opens directly. ## Option 2: open the mailbox file directly No add-on needed — Mbox Viewer opens Thunderbird’s extension-less mailbox files as-is, no renaming required: 1. **Quit Thunderbird** so the files aren’t in use. 2. In Finder, press `Cmd+Shift+G` and go to `~/Library/Thunderbird/Profiles/`, then into your profile’s `Mail/Local Folders/` directory. 3. **Copy** the mailbox file you want (e.g. `INBOX`) somewhere convenient, like your Desktop. Always copy — never move the original, or Thunderbird will lose track of it. 4. Open the copy with **Mbox Viewer** — double-click or drag & drop. No need to add a `.mbox` extension. ## What you get in Mbox Viewer Once open, you can [search with full query syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), browse conversations, preview [attachments](https://mboxviewerpro.com/glossary/attachment/) and export messages to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or plain text. Mbox Viewer is strictly **read-only**: your Thunderbird files are never touched, so the copy is purely a precaution. Files of any size work — a 20-year-old Inbox of 30 GB opens just as happily as a small archive, thanks to the [streaming parser](https://mboxviewerpro.com/glossary/streaming-parser/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # How to Open a Thunderbird MBOX File on Windows Thunderbird on Windows stores your mail as standard mbox files with no extension, tucked inside your profile folder. Here's how to find and read them with Mbox Viewer on Windows 10 and 11. PublishedJune 18, 2026 Mozilla Thunderbird has stored email in the open [**mbox**](https://mboxviewerpro.com/glossary/mbox/) format for over twenty years, so your Thunderbird mail on Windows is *already* in a format any standard reader can open. Two things trip people up on a PC: the mailbox files have **no extension**, and they’re hidden away inside the `AppData` folder that Windows keeps out of sight. This guide shows you exactly where to look and how to read them with Mbox Viewer. > Mbox Viewer for Windows is available on the [**Microsoft Store**](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) — install it and follow the steps below. ## Where Thunderbird hides your mail on Windows Each mailbox (Inbox, Sent, your custom folders…) is a single mbox file inside your Thunderbird profile: ``` %APPDATA%\Thunderbird\Profiles\.default-release\Mail\Local Folders\ ``` The quickest way there: press `Win + R`, paste `%APPDATA%\Thunderbird\Profiles` and hit Enter — File Explorer opens right inside it. (`%APPDATA%` expands to `C:\Users\\AppData\Roaming`, which is hidden by default, so the `Win + R` shortcut saves you from un-hiding folders.) Inside `Mail\Local Folders\` you’ll see files named `Inbox`, `Sent`, `Archives` and so on **with no extension**, each paired with a `.msf` file of the same name. The `.msf` files are just Thunderbird’s index — ignore them. The extension-less files are your actual mail, in standard mbox format. Mail tied to an IMAP account lives under an `ImapMail\` folder instead. ## Option 1: export with ImportExportTools NG (recommended) The free [ImportExportTools NG](https://addons.thunderbird.net/thunderbird/addon/importexporttools-ng/) add-on is the tidiest route and works the same on Windows as anywhere: 1. In Thunderbird, install **ImportExportTools NG** from the Add-ons Manager. 2. Right-click any folder → **ImportExportTools NG → Export folder**. 3. Choose a destination — you get a proper `.mbox` file. 4. Open it with **Mbox Viewer**: double-click in File Explorer or drag it onto the window. ## Option 2: open the mailbox file directly No add-on needed — Mbox Viewer reads Thunderbird’s extension-less files as-is: 1. **Close Thunderbird** so the files aren’t locked. 2. Open the profile folder with the `Win + R` trick above and go into `Mail\Local Folders\`. 3. **Copy** the mailbox you want (e.g. `Inbox`) to somewhere easy like your Desktop. Always copy — never move the original, or Thunderbird loses track of it. 4. In Mbox Viewer, use **File → Open** and pick the copy. No need to add a `.mbox` extension. ## What you can do once it’s open You can [search with the full query syntax](https://mboxviewerpro.com/guides/search-syntax-cheat-sheet/), follow threaded conversations, preview [attachments](https://mboxviewerpro.com/glossary/attachment/) and export to [EML](https://mboxviewerpro.com/glossary/eml/), CSV or plain text. Mbox Viewer is strictly **read-only**, so your Thunderbird data is never altered. Even a 20-year-old, 30 GB inbox opens smoothly thanks to the [streaming parser](https://mboxviewerpro.com/glossary/streaming-parser/). New to the format? Start with [how to open an MBOX file on Windows](https://mboxviewerpro.com/guides/how-to-open-mbox-file-on-windows/). ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB) --- [All guides](https://mboxviewerpro.com/guides/) # Mbox Viewer Search Syntax Cheat Sheet A complete reference for searching MBOX and EML archives in Mbox Viewer: from:, to:, subject:, body:, date:, has:attachment, size:>, OR, negation, and exact phrases — with copy-ready examples. PublishedMay 21, 2026 Mbox Viewer’s search bar understands a compact query language modeled on the operators power users already know from Gmail. This cheat sheet covers every operator, how to combine them, and ready-to-use examples you can paste straight into the search field. ## How search works Type a query into the search bar and Mbox Viewer filters the open archive in real time — even across millions of messages. A bare word like `invoice` matches anywhere in the message. To be precise, add **operators** in the form `field:value`. - Operators are **case-insensitive** (`From:` and `from:` are identical). - Multiple terms are joined with **AND** by default. - There’s no need to re-index between searches; results update as you type. ## Field operators | Operator | Matches | Example | | --- | --- | --- | | `from:` | The sender address or name | `from:alice@example.com` | | `to:` | A recipient (To field) | `to:team@example.com` | | `cc:` | A carbon-copy recipient | `cc:manager@example.com` | | `subject:` | Text in the subject line | `subject:invoice` | | `body:` | Text in the message body only | `body:"wire transfer"` | | `date:` | Messages on or around a date | `date:2025-03-14` | | `has:attachment` | Messages that carry a file | `has:attachment` | | `size:>` | Messages larger than a size | `size:>10mb` | | `size:<` | Messages smaller than a size | `size:<100kb` | ## Combining terms ### AND (the default) Listing terms together requires *all* of them to match. ``` from:alice subject:report has:attachment ``` Finds messages from Alice, with “report” in the subject, that include an attachment. ### OR Use `OR` (uppercase) to match *either* term. ``` from:alice OR from:bob ``` Returns messages from Alice **or** Bob. ### Negation Prefix a term with `-` to **exclude** it. ``` subject:invoice -from:noreply@example.com ``` Finds invoice subjects but hides the automated no-reply sender. ### Exact phrases Wrap words in quotes to match the **exact phrase** in order. ``` subject:"final invoice 2025" ``` Without quotes, the words could appear separately and in any order. ## Working with dates The `date:` operator accepts ISO-style dates and ranges. | Goal | Query | | --- | --- | | A specific day | `date:2025-03-14` | | On or after a date | `date:>=2025-01-01` | | Before a date | `date:<2025-06-01` | | A range | `date:2025-01-01..2025-03-31` | ## Working with size Size filters accept `kb`, `mb`, and `gb` suffixes. They’re perfect for finding the heavy messages eating up your archive. ``` has:attachment size:>25mb ``` ## Putting it together: practical recipes | Goal | Query | | --- | --- | | Find big invoice attachments | `subject:invoice has:attachment size:>5mb` | | All mail from two clients last quarter | `(from:acme OR from:globex) date:2025-04-01..2025-06-30` | | Exact-phrase contract mentions | `body:"master service agreement"` | | Newsletters to clean out | `from:newsletter -has:attachment` | | Large messages from anyone | `size:>20mb` | | A person’s mail, excluding receipts | `from:sam@ -subject:receipt` | ## Tips for faster searching - Start broad, then **add operators** to narrow results instead of retyping. - Combine search with **export** — filter first, then export the results to CSV or EML. - Use quotes whenever word order matters, especially for names and phrases. ## Search any archive, instantly These operators work the same whether your file is 5 MB or 50 GB. Open your [MBOX](https://mboxviewerpro.com/glossary/mbox/) and start searching. [Get Mbox Viewer on the Mac App Store →](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) ## Open your archive with Mbox Viewer Native Mac and Windows app. Streams MBOX and EML files of any size, fully offline. [Mac App Store](https://apps.apple.com/app/mbox-viewer-pro/id6759237715) [Microsoft Store](https://apps.microsoft.com/store/detail/9NW3GVFG7DDB)