.MBOX File Extension

Email Mailbox

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Category Text Files
Format Text

What is an MBOX file?

An MBOX file is an email mailbox, saved in a mail storage format that lists an entire inbox's messages in a single text file. It saves messages in a concatenated format where each message is listed after another, starting with the From header. MBOX files were originally used only by Unix hosts, but other email applications, including Apple Mail and Mozilla Thunderbird, now also support them.

More Information
Screenshot of a .mbox file in Apple Mail
MBOX file open in Apple Mail

Version 1.x of Apple Mail used MBOX files and stored them in the /​User/​Library/​Mail/​Mailboxes/​ directory. Mail 2.0 and later versions use the .EMLX format, which separates messages into individual files so they can be searched by Spotlight.

However, Apple Mail still exports mailboxes as MBOX files. If you right-click a mailbox and select Export Mailbox..., Apple Mail will save that mailbox's contents as an MBOX file.

NOTE: Opera Mail, which was discontinued in 2016, also stored messages in the MBOX format.

Common MBOX Filenames

INBOX.mbox - The name given to the primary Inbox mail folder in Apple Mail, macOS's default email program.

How to open an MBOX file

Because MBOX files are plain text files, you can open them in any text editor, such as Microsoft Notepad, Apple TextEdit, or GitHub Atom, to view their contents.

How to import MBOX files into Apple Mail and Mozilla Thunderbird

You can also import an MBOX file into Apple Mail or Mozilla Thunderbird, to view the messages the file contains in your email client.

To import an MBOX file into Apple Mail, select File → Import Mailboxes and then follow the prompts to import your MBOX file. The messages your MBOX file contains will appear in the Import mailbox.

To import an MBOX file into Mozilla Thunderbird, you must first install the ImportExportTools NG add-on. Then, open Thunderbird and select Tools → ImportExportTools → Import MBOX File and follow the prompts to import your MBOX file. The messages your MBOX file contains will appear in the Local Folders inbox.

How to convert an MBOX file

Several conversion utilities allow you to convert MBOX mailboxes to the .PST format used by Microsoft Outlook. Some examples include:

  • Regain MBOX to PST Converter
  • EdbMails
  • Aryson MBOX to PST Converter
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Programs that open MBOX files

Updated April 12, 2022

Verified by FileInfo.com

The FileInfo.com team has independently researched the Email Mailbox file format and Mac, Windows, and Linux apps listed on this page. Our goal is 100% accuracy and we only publish information about file types that we have verified.

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