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Format

MBOX

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Summary

Name
MBOX
Identifiers
  • MIME: application/mbox
  • PUID: fmt/720
Format type
Text (Structured)
Description
MBOX is a commonly used format for storing email messages. MBOX files may be produced by a variety of email clients, however these are often not mutually compatible. MBOX databases typically contain a linear sequence of electronic mail messages. Each message begins with a separator line that identifies the message sender, and also identifies the date and time at which the message was received by the final recipient (either the last-hop system in the transfer path, or the system which serves as the recipient's mailstore). Each message is typically terminated by an empty line. The end of the database is usually recognized by either the absence of any additional data, or by the presence of an explicit end-of-file marker. Attachments within MBOX files are typically base 64 encoded, allowing binary data to be transferred over media designed to deal with textual data. Due to the variety of MBOX structures, it is not currently possible to produce an authoritative signature for the format.
File extensions
mbox
Submitted by
Digital Preservation Department / The National Archives

Relationships

Has priority over

Internal signatures

MBOX

Description
Based on https://www.rfc-editor.org/rfc/rfc4155, BOF: ASCII string 'From ' , followed by a {1-255} wildcard in place of a sender identifier or system message, followed by a ctime-format timestamp comprising an English-language three-character weekday abbreviation (Mon|Tue|Wed|Thu|Fri|Sat|Sun), three-character month abbreviation (Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec), day-of-month digit, and time in HH:MM:SS format.
Provenance
Note that this identification pattern has been tested with Gmail and Thunderbird-produced MBOX files and should suit all MBOX files produced following the established UNIX pattern described here: http://qmail.org./man/man5/mbox.html however there may be other variants that differ in implementation.

Byte sequences

Min Frag Length
Absolute from BOF
Offset
0
Max offset
0
Byte Sequence
46726F6D20{1-255}(4D6F6E|547565|576564|546875|467269|536174|53756E)20{0-2}(4A616E|466562|4D6172|417072|4D6179|4A756E|4A756C|417567|536570|4F6374|4E6F76|446563)20{0-2}[30:39]20[30:32][30:39]3A[30:35][30:39]3A[30:35][30:39]
Endianness
None

Changelog

  • V125

    Release date
    7 September 2026

    • Updated

      MBOX: Priority over fmt/950 MIME Email added. Submitted by Preservica.

  • V123

    Release date
    9 June 2026

    • Added signature

      MBOX: Signature researched and samples provided by Preservica.

    • Updated

      MBOX: New binary signature created and priority added over fmt/950 MIME Email 1.0. Submitted by Preservica.

  • V81

    Release date
    18 February 2015

    • Added format

      MBOX: Full entry added.