An export is a photograph of your mailbox on one day; a backup is a copy that keeps up. Google Takeout, Apple Mail’s export or a copied Thunderbird profile give you an MBOX file of everything up to the moment you made it — and nothing after. Whatever arrives and gets deleted between two exports is in neither. This guide sets up the other kind: a scheduled copy of the account, on your own disk, as plain MBOX files that Mbox Viewer opens like any other.

We use Arca Mail Backup, our backup app for Mac and Windows, because it writes exactly the format this site is about. The free plan is enough for everything below.

Takeout or a scheduled backup?

They do different jobs, and many people need both.

An export (Takeout, Apple Mail, Thunderbird) is right for an account you are about to close, one you no longer use, or a one-off archive. It needs no software installed and nothing running.
A scheduled backup is right for an account you still use. It runs on its own, and it does something an export cannot: a message deleted on the server stays in the backup, marked as deleted, instead of disappearing from it too. That is the difference between a copy and a history, and the reason a mailbox that only lives on the server is not the same as a copy you own.

What you need

A Mac with macOS 14 or later, or a PC with Windows 10 or 11.
The account’s address and a way to sign in to it:
- Gmail or Google Workspace: an app password, which Google only offers when 2-Step Verification is on. On Workspace, your administrator has to allow IMAP and app passwords.
- Outlook.com, Hotmail or Microsoft 365: your Microsoft sign-in, done in the browser. A work or school account may need your organisation to approve Arca first.
- Any other provider: the IMAP server, port (usually 993), user name and password, all of which are in your provider’s help pages.
A folder on an internal or external disk with room for the mailbox.

The app’s interface is in English and Spanish; the steps below quote the English labels.

Step 1: Install Arca Mail Backup

Get it from the Mac App Store or the Microsoft Store. On first launch you see Welcome to Arca Mail Backup.

Leave Back up in the background switched on. On a Mac it adds Arca to your Login Items; on Windows it adds it to your startup apps and puts an icon in the notification area. Either way, backups run on schedule even when the window is closed. Without it, Arca only copies when you press Back Up Now. Then click Get Started.

Step 2: Add your account

Type the address under Email and click Continue — Arca works out how to connect from the address, and you can correct it in the Provider menu: Gmail or Google Workspace, Outlook.com or Microsoft 365, or Other (IMAP).

Gmail: follow Create an app password in your Google account, copy the 16-letter password Google shows you and paste it into App password, with or without the spaces. Your real Google password is never shared with the app.
Outlook / Microsoft 365: click Sign In with Microsoft and finish in the browser. Arca never sees your password; Microsoft grants it permission to read your mail over IMAP, and you can revoke that from your Microsoft account at any time.
Other (IMAP): fill in Server, Port, User name and Password, then Test Connection.

Once it says Connected to…, choose the folders under Which folders should Arca back up? and click Continue. For Gmail, Arca copies All Mail with its labels, so a message with three labels is stored once rather than three times.

Step 3: Choose where to save the backup

Under Where should Arca save your mail?, pick A folder or external disk and choose the folder. Arca writes a test file and shows Write test passed if it can use it.

An external drive is the better choice if you have one: a copy on the same disk as the computer dies with the computer. On the free plan the destination has to be a disk of this computer, internal or external; a NAS, an S3-compatible bucket, a folder synced to a cloud drive or several destinations at once are part of Arca Pro.

Step 4: Set the schedule and make the first copy

Under How often should Arca back up?, choose a Frequency. The free plan backs up once a day at most — Daily is the sensible choice; Arca Pro adds every 1, 3, 6 or 12 hours. On a laptop, Only when connected to power keeps it from running on battery.

Click Start First Backup. The first one is the slow one, because it copies the whole mailbox; after that, each run only fetches what changed. A large Gmail account can take several days for the first copy, because Google limits how much an account can download per day. If it is interrupted — the laptop sleeps, the Wi-Fi drops — the next run carries on from where it stopped.

Step 5: Check the backup with Mbox Viewer

Do not take the backup on trust: open it. In the folder you chose, Arca creates an arca folder and, inside it, one folder per computer. The mail is stored as one MBOX file per folder and month:

arca/<computer>/accounts/<account>/folders/<folder>/2026/2026-10.mbox

For a Gmail account, <account> is the address with symbols turned into dashes (you-gmail-com) and <folder> is gmail-all-mail. Next to accounts there is a manifest.json, a copy of the index and a README.txt that explains how to open everything without Arca.

Drag one of those .mbox files onto Mbox Viewer — on Mac or on Windows — and search for a message you know is from that month. Monthly files stay small, so they usually fit within the free version’s 1 GB limit. To read a whole year in one window, Mbox Viewer can merge several months into one file.

Mbox Viewer only reads the file; it never writes to it, so checking the backup cannot damage it. Months that are already closed are not touched again by Arca either.

Getting back a message that was deleted on the server

This is what the backup is for. In Arca, search by subject, sender, recipient or text across every account. A message that no longer exists on the server carries the badge Deleted on server.

Select it and choose Restore Selected…. The messages come back into a New folder of the same account — by default called Restored Arca plus the date — and nothing already on the server is changed. Also restore what is still on the server is off by default, so only what was deleted comes back and you get no duplicates. Restoring into the same account is free.

If you only need the message as a file, Export .eml… saves it on its own.

Already have a Takeout or an old MBOX?

Arca also takes in the archives you already have. Import an .mbox File… reads Google Takeout (keeping the labels), Thunderbird profile folders, Apple Mail .mbox packages and any standard MBOX, and turns them into an offline account you can search alongside the live ones. Imported mailboxes do not count towards the free plan’s one account. It does not import PST or EML; for Outlook files, convert them to MBOX first.

Free plan and Arca Pro

The free plan covers one connected account, backed up in full to a disk of your computer once a day, with search, checks, import and restoring into the same account included and no size limit. Arca Pro adds more accounts, NAS and S3 destinations, several destinations at once, backups every few hours and restoring into a different account. Prices and the full comparison are on arcamailbackup.com.

Whichever plan you use, the files are standard MBOX on your disk: if you stop using Arca tomorrow, the backup still opens in Mbox Viewer, Thunderbird or any other reader.

How to Back Up Your Email Automatically to MBOX (Mac and Windows)