Mailbox File
An MBOX file is an email mailbox archive format that stores multiple email messages in a single plain text file. Standardized in RFC 4155, it concatenates messages separated by "From " lines.
This format is not currently supported for conversion in FileDex.
Common questions
What is an MBOX file?
An MBOX file is a mailbox archive that stores multiple email messages sequentially in a single plain text file, separated by "From " delimiter lines.
How do I open an MBOX file?
Open MBOX files with Mozilla Thunderbird (via ImportExportTools NG addon), Apple Mail (File > Import Mailboxes), or dedicated viewers like MBox Viewer and Mailspring.
How do I convert MBOX to individual emails?
Use Thunderbird with the ImportExportTools NG addon to import the MBOX and export individual messages as EML files, or use command-line tools like formail or mb2md.
What makes .MBOX special
The MBOX format originated in early Unix mail systems and has evolved into several variants including mboxrd, mboxcl, mboxcl2, and mboxo, each handling the "From " line escaping differently. In the most common variant (mboxrd), each message begins with a line starting with "From " followed by the sender address and timestamp, and subsequent occurrences of "From " at the start of message body lines are escaped with a leading greater-than character. MBOX files preserve complete RFC 2822 message headers and MIME-encoded content including attachments. The format is used by Thunderbird, Apple Mail, many Unix mail tools, and Google Takeout for Gmail exports. While simple and universally supported, MBOX has limitations for concurrent access since the entire file must be locked for write operations, which led to the development of the Maildir format for server-side storage.
Continue reading — full technical deep dive
Related Formats
Technical reference
- MIME Type
application/mbox- Developer
- Various
- Year Introduced
- 1975
- Open Standard
- Yes — View specification