--- title: "Where Thunderbird Keeps Your Email — Mbox Viewer" description: "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." url: https://mboxviewerpro.com/blog/where-thunderbird-keeps-your-email/ language: en updated: 2026-09-07 source: Mbox Viewer --- [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)