MBOX file icon

MBOX File Extension

E-mail Mailbox Format

What is MBOX file?

File with .MBOX extension contains an email message box file which stores list of messages for given recipient in sequential order. MBOX is a text file, and each message referenced in such file starts with ‘From’ header and ends with newline character. MBOX format is not standardized in any RFC document and as such its structure largely depends on the software that uses this format for archiving email messages.

MBOX files (referred to as MailBOX) were first used by a simple Unix mail client. Mac OS, which is based on Unix, used the MBOX format for its first mail client. The format has many disadvantages, some of them being:

  • Lack of message encryption,
  • Sequential read from a single file, even for large number of messages – parsing issues,
  • Any user that has access to given MBOX file can read stored messages,
  • File locking mechanism must be employed in order to ensure file integrity when multiple users access the mail file simultaneously.

MBOX format was the base for 4 other mailbox formats – mboxo, mboxrd, mboxcl, and mboxcl2. Those formats are not compatible with each other, although all are based on MBOX. MBOX text files can be opened with any text editor, but editing such files is not advised as it may caused read errors.

Programs which support MBOX file extension

The following list contains programs grouped by 3 operating systems that support MBOX files. Files with MBOX suffix can be copied to any mobile device or system platform, but it may not be possible to open them properly on target system.

Programs that support MBOX file

Updated: 01/12/2024

How to open file with MBOX extension?

Problems with accessing MBOX may be due to various reasons. Fortunately, most common problems with MBOX files can be solved without in-depth IT knowledge, and most importantly, in a matter of minutes. We have prepared a listing of which will help you resolve your problems with MBOX files.

Step 1. Download and install Mozilla Thunderbird

Install software to open MBOX file The main and most frequent cause precluding users form opening MBOX files is that no program that can handle MBOX files is installed on user’s system. The most obvious solution is to download and install Mozilla Thunderbird or one to the listed programs: Apple Mail, Eudora, Microsoft Outlook. Above you will find a complete listing of programs that support MBOX files, classified according to system platforms for which they are available. If you want to download Mozilla Thunderbird installer in the most secured manner, we suggest you visit Mozilla Corporation website and download from their official repositories.

Step 2. Verify the you have the latest version of Mozilla Thunderbird

Update software that support file extension MBOXIf the problems with opening MBOX files still occur even after installing Mozilla Thunderbird, it is possible that you have an outdated version of the software. Check the developer’s website whether a newer version of Mozilla Thunderbird is available. It may also happen that software creators by updating their applications add compatibility with other, newer file formats. This can be one of the causes why MBOX files are not compatible with Mozilla Thunderbird. All of the file formats that were handled just fine by the previous versions of given program should be also possible to open using Mozilla Thunderbird.

Step 3. Set the default application to open MBOX files to Mozilla Thunderbird

If you have the latest version of Mozilla Thunderbird installed and the problem persists, select it as the default program to be used to manage MBOX on your device. The method is quite simple and varies little across operating systems.

Associate software with MBOX file on Windows

The procedure to change the default program in Windows

  • Clicking the MBOX with right mouse button will bring a menu from which you should select the Open with option
  • Select Choose another app → More apps
  • To finalize the process, select Look for another app on this PC entry and using the file explorer select the Mozilla Thunderbird installation folder. Confirm by checking Always use this app to open MBOX files box and clicking OK button.
Associate software with MBOX file on Mac

The procedure to change the default program in Mac OS

  • Right-click the MBOX file and select Information
  • Find the Open with option – click the title if its hidden
  • Select Mozilla Thunderbird and click Change for all...
  • If you followed the previous steps a message should appear: This change will be applied to all files with MBOX extension. Next, click the Continue button to finalize the process.

Step 4. Ensure that the MBOX file is complete and free of errors

Should the problem still occur after following steps 1-3, check if the MBOX file is valid. It is probable that the file is corrupted and thus cannot be accessed.

Check MBOX file for viruses
1. Check the MBOX file for viruses or malware

If the file is infected, the malware that resides in the MBOX file hinders attempts to open it. Scan the MBOX file as well as your computer for malware or viruses. If the MBOX file is indeed infected follow the instructions below.

2. Ensure the file with MBOX extension is complete and error-free

If the MBOX file was sent to you by someone else, ask this person to resend the file to you. It is possible that the file has not been properly copied to a data storage and is incomplete and therefore cannot be opened. If the MBOX file has been downloaded from the internet only partially, try to redownload it.

3. Verify whether your account has administrative rights

Some files require elevated access rights to open them. Log out of your current account and log in to an account with sufficient access privileges. Then open the E-mail Mailbox Format file.

4. Make sure that the system has sufficient resources to run Mozilla Thunderbird

If the system is under havy load, it may not be able to handle the program that you use to open files with MBOX extension. In this case close the other applications.

5. Check if you have the latest updates to the operating system and drivers

Up-to-date system and drivers not only makes your computer more secure, but also may solve problems with E-mail Mailbox Format file. It may be the case that the MBOX files work properly with updated software that addresses some system bugs.

Conversion of a MBOX file

File Conversions from MBOX extension to a different format
File conversions from other format to MBOX file
Do you want to help?

If you have additional information about the MBOX file, we will be grateful if you share it with our users. To do this, use the form here and send us your information on MBOX file.

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