What is a MBOX File? Everything You Should Know

Admin | August 20th, 2016 | Computer, Email, Technology

What is MBOX?

MBOX is a format that is most commonly used for storing email messages on the memory storage. MBOX holds a large collection of files of email messages. There are many email clients which uses MBOX format to store its files. The email clients like Apple mail, Microsoft entourage, Mozilla Thunderbird and Qualcomm Eudora uses MBOX to store and manage its data files. It allows you to hold list of emails related to your business and others. The MBOX stores the mailbox messages in their original internet message format. It stores all the messages in a single database every new message is appended to the end of the file. Each line of message is prefaced by a separation line and terminated by an empty line.


Structure of a MBOX File:

The MBOX file uses a predefined format to store the messages. A message encoded in MBOX format begins with a from_line, continues with series of non from_lines and ends with blank line. A from_line means any line that begins with the characters F, r,o,m space. The format is

From <sender name> <date> <moreinfo>

<Sender name> It is the name of the sender in one word without spaces or tabs.
<Date> It is the delivery date of the message.
<More info> It is the information in the message.

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FROM: Jane Wed Oct 5 01:06:54 2000
From: jane@example.com
To: Receipt receipt@example.com
Subject: <message description>

<Body of the message>


Types of MBOX Files
A lot of emailing application uses MBOX as the format to save the data but the some of the saved them with MBOX as file extension but some saves it without any MBOX file extension. So, it is quite possible that your MBOX file may not have any file extension and it will appear as a simple .txt file.


There are four variants of MBOX they are,

MBOXO format starts scanning for From lines that are found before the email messages headers. If a “from” string occurs at the beginning of a line either the header or the body of a message the email message must be modified before storing the message in the MBOX or the line will be taken as the start of a new message. The MBOXO mails prepends > symbol to any line of the message either in the header or body.

Example: >From

MBOXRD was designed to solve the message corruption problem found in MBOXO format. It employs reversible from quoting because it allows for differentiating between “>From” found in original message and”>From” found in a transformed MBOXO file. This acts as a separator between email messages. The transformation is always reversible.

Example: From to >From and >From to >>From

MBOXCL & MBOXCL2 uses irreversible quoting where it prepends > sign before the “From” string whenever it occurs at the beginning of a line either in the header or body of the message. It does not scan “From” to determine the separator points. MBOXCL-here CL stands for content length. It contains header that determines the length of the messages. The header is added to the message when it is added to the mailbox it is used to locate the start of each message.

Though MBOX file is used to store and manage the mails but MBOX stores entire folder in one file hence the size of the MBOX file can be large.