What is MBOX File Format?

MBOX is a common file format that carries out electronic mail messages on a local hard disk. All messages are concatenated in plain text format and are stored in a single, long text file initializing with "From" and "Sender's mail address". The closing of each message is specified by blank lines connected to the end.

MBOX stands fro MailBOX and is one of the most popular file formats, which is supported by several email clients like Thunderbird, Apple Mail, Entourage, Eudora, etc. MBOX format was used primarily on the UNIX system. This file format can be used for saving and managing emails in the database.

MBOX File Specifications

Introduced by Berkeley Mail
Format Type 7-bit ASCII text
File Category Database & Email
Supported Platform MS Windows, Mac, Unix-like Systems
MIME Type text/x-mailbox
File Signature Hex Signature: 00 0D BB A0

Learn About the Different Versions of MBOX File

The basic MBOX structure is categorized into four parts and are separated by changes to "From" line and the usage of "message body Length:" field in the message header to decide the beginning of another message inside a combined document. Moreover, the variants and apparatus sets are not well-suited with another version. In addition to this, MBOX documents include email attachments, in a unique MIME format.

  • Mboxo: It is the first form of MBOX file in which a constant string like "....@...." is used instead of sender's mail address.
  • Mboxrd: It is different from Mboxo mailbox format. The beginning of message is exhibited by "From" string to the start of a line in either header or body of the message.
  • Mboxcl: This file format is used by Unix 'System V' mail account. If any mail should be added to "mboxcl" mailbox document, it has changed before annexing to a record.
  • Mboxcl2: This file format is similar to Mboxcl. It cannot change before a message is being added to mboxcl2 format.

Know Where Are MBOX Files Located

The MBOX files are located at the default location:


This position varies according to the different email clients.

Supported Email Applications

There are multiple email clients which saves and stores the emails in MBOX file format or its variants. Some of the more popular ones are as follows:

  • Mozilla Thunderbird
  • Apple Mail
  • Eudora
  • Entourage
  • Pocomail
  • Opera Mail
  • Spicebird Mail
  • Netscape, and so on...