MBOX File Extension – What is an MBOX File?

Summary: MBOX is a well-known file format used by numerous email clients to save emails, contacts, attachments, and more. In this post, we’ve discussed the MBOX file in detail, its structure, and location. We’ve also mentioned a software to convert MBOX file to PST, in case you want to migrate from MBOX-based email client to Outlook.

MBOX File Extension – What is an MBOX File?

MBOX, also called Mail Box file, is a collection of electronic mail messages saved in ASCII text. MBOX files were first used by Unix hosts. These files are now supported by Apple Mail, Spicemail, Entourage, Pocomail, and Mozilla Thunderbird, among other email clients. The file saves the entire folder’s email messages in a single database file which contains one email after another and the attachments in an encoded format.

MBOX File Structure

MBOX file stores the messages in plain text form. Each message in the MBOX file starts with a new line that includes the sender’s name, along with date and time of the received message. There are different MBOX file formats. Let’s take a look at them:

  • MBOXO: It is different from the original MBOX file format. It uses the constant string, such as “???@???” instead of the sender’s mail address.
  • MBOXRD: It is another type of MBOX file format that is used to hold electronic mail messages.
  • MBOXCL: This type of file format is used by the Unix ‘System V’ mailboxes.
  • MBOXCL2: This file format is same as MBOXCL. It is not possible to convert before a message is appended to the MBOXCL2 mailbox file.

MBOX File Location

MBOX is saved at a default location on the system. Usually, the MBOX file location depends upon the operating system and the email client you’re using. The default location of MBOX file is:  


Issues You May Encounter With MBOX Files

While accessing the MBOX files, you may encounter some issues. Some of the common issues are:

  • Emails Do Not Open: When opening an MBOX email, you may receive an error message stating that the MBOX file is not available or moved from the location.
  • MBOX File Becomes Oversized: When the MBOX file becomes large in size, you may face difficulty in sending and receiving the mails. Also, it takes a lot of time to load new emails.
  • Cannot Open .MBOX File: Sometimes, you may not be able to access your .MBOX files due to some unexplained factors.
  • Platform Dependency: All the MBOX supporting email clients are desktop-based. So, the entire database is saved at the local storage. Hence, the mailbox messages can only be accessed at the same desktop where the MBOX file is saved.
  • No Valid MBOX File Found: You may receive this error while trying to access a wrong directory. Sometimes, the external storage device, wherein the MBOX file is saved, becomes corrupt, resulting in this error.

How to Import MBOX Files into Outlook?

If you want to migrate from MBOX-based email client to Outlook, you need to convert the MBOX file into PST file format as Microsoft Outlook does not support the MBOX file format. After converting the MBOX file into PST, you can import this PST file into any Outlook account.

The best and easiest way to convert MBOX file to PST is by using a professional MBOX to PST converter software, such as Stellar Converter for MBOX. The software can convert MBOX file of all popular MBOX-based email clients to PST and other formats in a few simple steps.

Steps to convert MBOX file to PST by using the software:

  • Download, install, and launch the software.
  • From the main interface, select mail client from the dropdown list.
  • Click the ‘Select File’ button to select the MBOX file you want to convert or use the ‘Select Identity’ button to select the identity folder containing MBOX files. Then, click ‘Convert’ to begin the converting process.

Note: If you don’t know the MBOX files location, you can use the software’s “Find File” feature to find them.

Home Sreen Mbox Converter
  • The software starts the MBOX to PST file conversion process. When the conversion process is finished, the MBOX file’s mailbox items are displayed in a tree-view format. You can see the preview of any item by clicking on it.
Preivew Items Page
  • After previewing the items, go to the Home tab and select the ‘Save Converted File’ option. A ‘Save As’ dialog box appears with options for saving the file (New PST, Existing PST, EML, and MSG). Choose the appropriate saving option and then press the ‘Next’ button.
Saving Converted File Options
  • In the ‘Choose Destination’ window, click ‘Browse’ to select the file saving location on your system. Then press the ‘Save’ button.
Browse Path to Save File
  • When the data is successfully saved, a message box appears. Click OK.
Conversion Complete Dialog Box

You can now import the PST file into Outlook by using the Import/Export Wizard.


MBOX files are supported by many leading emails clients, such as Mozilla Thunderbird, Apple Mail, Pocomail, etc. If you want to migrate from MBOX-based email client to Outlook, you need to first convert the MBOX file to Outlook PST format and then import the PST file into Outlook. To quickly and easily convert MBOX to PST, you can use the Stellar Converter for MBOX software. The software converts MBOX file to PST and various other formats. It also allows you to save the converted file directly to Office 365. You can download the free version of the software to evaluate its functionality and effectiveness.

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