How to open a .mbox file
Mailbox archive · Email
An .mbox file is an entire mailbox stored as one plain-text file. Thunderbird imports it, and because it is text you can open it in an editor to confirm what is inside.
What a .mbox file actually is
MBOX concatenates every message in a folder into a single file, each one starting with a line beginning "From ". It is the classic Unix mailbox format and remains the standard export format for Gmail via Google Takeout.
That is why most people meet it: they download their Gmail archive, get a multi-gigabyte .mbox, and discover nothing on their computer will open it.
Why it will not open
No desktop mail client claims the .mbox extension by default, and the files are frequently enormous, so a text editor either refuses or freezes trying to load the whole thing into memory.
Step by step
Windows
- 01Install Thunderbird, which is free.
- 02Add the ImportExportTools NG add-on, then use Tools, ImportExportTools NG, Import mbox file.
- 03Choose the .mbox and let it index. With a large Gmail archive this can take a long time; leaving it running is normal.
- 04The messages then appear as an ordinary folder you can search and read offline.
macOS
- 01Apple Mail imports MBOX natively: File, Import Mailboxes, then choose "Files in mbox format".
- 02Thunderbird works identically to Windows if you prefer it.
What usually goes wrong
Gmail Takeout produces one huge file
A full Gmail export easily reaches several gigabytes in a single .mbox. Do not try to open it in a text editor. Import it into Thunderbird or Apple Mail, which read it incrementally instead of loading it all at once.
Programs that open .mbox
Our pick, in order. Every one links to the publisher's official download URL and the SHA-256 hash of the installer, so you can check the file before you run it.
Common questions
- How do I open an MBOX file from Gmail Takeout?
- Import it into Thunderbird using the ImportExportTools NG add-on, or into Apple Mail via File, Import Mailboxes. Both read the archive incrementally, which matters because Gmail exports are often several gigabytes.
- What is the difference between MBOX and EML?
- An EML holds one message. An MBOX holds an entire folder of messages concatenated into a single file. Both are plain text, so both are readable, but MBOX needs a mail client to be usable.