MBOX File Extension

Get deep information about MBOX file extension

mbox file extension

Desktop based email clients have become more than just a way to read, write and receive mails. Nowadays, email applications are renovating into tremendous productivity tools, which permit users to easily manage email with a little effort and customized to user’s email requirement by offering beneficial features. Each email client has different file extension to store its database. Out of which one of them is MBOX file extension.

MBOX file extension is a plain text file that saves email data as 7 bit ASCII text and all the attachments are saved in encoded format. Mainly, MBOX files are used for storing or managing the messages in single text files that stands for MailBox.  In it, each message is specified by “From” with a white space character and at the end of every message; it is specified with a blank line. In the following section we will discuss about MBOX file format.


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MBOX File Format Description

MBOX family includes numerous modified file formats: mboxo, mboxrd, mboxcl, and mboxcl2. These file formats will be clear to understand as mentioned:

  • mboxo: It uses constant strings i.e. “??@??” instead of an email address of sender.  Eudora is the best example of mboxo format. In it the messages are not stored intact as they received as the attachments in the mail are separated and stored as individual files in separate folder.
  • mboxrd: It is basically the variation of mboxo mailbox.  The beginning of message is indicated by a string “From” at starting of line in either body or header of message.  There is an email client qmail , which is famous for using mboxrd. However, there are other email applications such as Thunderbird, Netscape, etc. that support MUAs.
  • mboxcl:  This format of MBOX is utilized by the mailboxes of ‘UNIX System V.’  When new mail is appended to mboxcl mailbox, it is transformed to the file before appending. The message has a single character ‘>’ that is pre appended to any line of mail message in either body or header, which starts with 5 characters, i.e. F, r, o, m.  Content Length: header is used by mboxcl for locating start message.  It indicates the length of body of message after transformation. It helps to locate the beginning and end of mail message.
  • mboxcl2:  It is similar to mboxcl. It does not utilize “From quoting”, content length is also used to specify the of content. In it no transformation is done before appending the message to mailbox file.

Stored Location

MBOX stores all its data at default location   i.e. “/user/library/mail/mailboxes/directory”. The store location can vary for various MBOX based email application.

Supported Email Clients

MBOX file extension is supported by different email applications for the data management such as AppleMail, Mulberry, Entourage, Thunderbird, Eudora, Spicebird, SeaMonkey, Mozillamail, Pocomail, Netscape, ClawsMail, Cone, Evolution, Sylpheed, OperaMail, Mutt, Gnu Mail, etc.

Security Concerns

Security is the main concern of every user before accessing any email application. MBOX file extension is an open source file that can be easily open on any platform. Therefore user can easily access and edit the data. It offers profile protection security only. With the profile protection security they can provide password security.

However many times users face some issue while accessing MBOX file extension data, one such issue is discussed below that is taken from the forums site.

Problem Faced by Users

“I use Thunderbird as an email application on my system to manage all my data. As it supports MBOX file format that can be easily view on any text file. Therefore, I am planning to switch my email client because my mails contain all my organization’s data. Can anyone guide me a relevant solution to convert all my data from one email application to another?”


Users can use the third party utility to perform the conversion of data from one email application to another as it helps to save user’s time and effort by using few steps. It helps to maintain the data integrity.

  1. Launch and run the utility on your system
  2. Browse the file from stored location to begin the process
  3. After conversion completion, message will be displayed as conversion completed successfully


MBOX file extension is supported by various email clients for the storage of database. In the above discussion, MBOX file format description is discussed. Along with it, the problem faced by users by using MBOX file extension and its solution is described.