.mbox

What is a .mbox file?

MBOX is a file format that stores multiple email messages concatenated in a single text file.

Use caution
Type Document
By Unix (historical, no single creator)
MIME application/mbox

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What is it

An MBOX file is the simplest possible email archive — multiple email messages concatenated in a single text file, each separated by a 'From ' line. The format dates back to the earliest Unix mail systems and remains in use because of its sheer simplicity. Google Takeout exports your entire Gmail as an MBOX file.

The lack of structure is both a strength and weakness. MBOX files are easy to create, easy to parse, and readable in any text editor. But accessing a specific message in a large MBOX requires scanning through the entire file, and concurrent access is problematic. Maildir format solves these issues for servers, but MBOX persists for archival and export.

Thunderbird imports MBOX files natively (use the ImportExportTools add-on for direct import). Apple Mail can import MBOX via File → Import Mailboxes. For searching and browsing large MBOX archives, tools like mboxgrep (command-line) or Thunderbird's search work well.

Technical details
Full Name
Mailbox File
MIME Type
application/mbox
Developer
Unix (historical, no single creator)
Magic Bytes
N/A
Safety
.mbox requires caution. Contains email messages which may include malicious attachments or phishing content.
What opens it
Thunderbird (+ ImportExportTools)
FREE Windows / Mac / Linux
Apple Mail
FREE Mac
Any text editor
FREE Windows / Mac / Linux
FAQ
How do I open a Google Takeout MBOX file?
Import into Thunderbird using the ImportExportTools add-on: install the add-on, then use Tools → ImportExportTools → Import mbox file. Apple Mail can also import via File → Import Mailboxes.
Can I search inside an MBOX file?
After importing into Thunderbird or another email client, use the client's built-in search. For command-line searching, grep works since MBOX is plain text. For structured searching, mboxgrep parses the email structure.
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