What an MBOX file is and why you have one

An MBOX file is a single file that holds many emails in plain text format. Instead of storing each message separately like most email programs do, MBOX bundles them all together. You most often encounter MBOX files when you export emails from Gmail, Outlook, Apple Mail, or Thunderbird — or when someone sends you a backup of their email account.

The file itself looks like a single document with a .mbox extension. Opening it directly in a text editor will show you the raw email data, which is readable but messy. To see your emails the way you normally would — with subject lines, sender names, and attachments organized — you need to import the MBOX file into an email program that understands the format.

The simplest path depends on what email program you already use. If you have Thunderbird, Outlook, or Apple Mail installed, you can import directly. If you do not have an email program, you can install Thunderbird for free, which handles MBOX files natively.

Key Takeaways

  • MBOX files are email backups that hold many messages in one file and need to be imported into an email program to read properly.
  • Thunderbird, Outlook, and Apple Mail can all import MBOX files directly from their menu — no separate software needed.
  • If you do not have an email program installed, Thunderbird is free and opens MBOX files without any extra steps.
  • Opening an MBOX file in Notepad or Word shows the raw email code and is not the intended way to read the messages.

Opening MBOX files in Thunderbird

Thunderbird is a free email program from Mozilla that handles MBOX files directly. If you do not already have it, read Thunderbird from mozilla.org and install it on your computer. Once it opens, you will see a folder list on the left side.

Right-click on any folder in that list — usually "Local Folders" — and select "Import" from the menu. A window will open asking you to choose a file. Navigate to your MBOX file and select it. Thunderbird will read the file and place all the emails into that folder. You can then browse them normally, search them, and read attachments.

If you have many MBOX files to import, you can repeat this process for each one. Thunderbird will not delete the original MBOX file, so you can keep it as a backup.

Opening MBOX files in Outlook

Outlook on Windows and Mac can import MBOX files, but the process is slightly different from Thunderbird. Open Outlook and go to the File menu at the top. Look for an option called "Open & Export" or "Import" depending on your version.

Select "Import" and then choose "MBOX File" from the list of options. A dialog will ask you to locate your MBOX file on your computer. Select it and click through the prompts. Outlook will create a new folder with the emails from your MBOX file, usually labeled with the file name.

On Mac, the steps are similar: go to File, then Import, then select MBOX. The imported emails will appear in a new folder in your mailbox list.

Opening MBOX files in Apple Mail

Apple Mail on Mac can import MBOX files through its File menu. Open Apple Mail and click File at the top. Select "Import Mailboxes" from the dropdown. A window will open asking you to choose a file format — select MBOX.

Navigate to your MBOX file and select it. Apple Mail will import the emails into a new mailbox, usually named after the original file. The emails will appear in your sidebar under "On My Mac" or in your main mailbox list, depending on your Mail settings.

What to do if you only have a text editor

If you open an MBOX file in Notepad, Word, or another text editor, you will see the raw email data. This includes email headers, message bodies, and attachment code all mixed together. While you can read the text portions of emails this way, it is difficult and you will not see attachments properly.

This is not the intended way to read MBOX files. Instead, install one of the email programs mentioned above — Thunderbird is the easiest free option — and import the file there. You will have a much clearer view of your emails and can search, sort, and manage them like you would in any email inbox.

Converting MBOX to another format

If you need your emails in a different format — such as PST for Outlook or EML for individual message files — you can convert an MBOX file after importing it. Import the MBOX file into Thunderbird or Outlook first, then use that program's export function to save the emails in a new format.

In Thunderbird, right-click the folder containing your imported emails and select "Export" to save as EML files. In Outlook, select the emails you want to export, go to File, and choose "Save As" to create a PST file. This two-step process — import then export — is the most reliable way to change formats.

Troubleshooting common problems

If Thunderbird or Outlook does not recognize your MBOX file, check that the file extension is actually .mbox and not something else like .txt or .mail. Some email programs save backups with different extensions even though the content is MBOX format. Renaming the file to end in .mbox often fixes the problem.

If the import starts but stops partway through, the MBOX file may be corrupted or very large. Try importing it again, or break it into smaller pieces if possible. Some email programs have trouble with MBOX files larger than a few hundred megabytes. If you exported the file from Gmail or another service, check whether that service offers a way to export in smaller batches.

If you imported the file but do not see the emails, check that you are looking in the right folder. Imported emails often go into a new folder rather than your inbox. Look in the folder list on the left side of your email program for a folder with the MBOX file name.

Frequently Asked Questions

Can I open an MBOX file on my phone?

Most phone email apps do not support MBOX files directly. Your best option is to import the MBOX file into Thunderbird or Outlook on your computer first, then sync those emails to your phone through your email account. Some third-party apps claim to open MBOX files on Android or iPhone, but they are unreliable and often require payment.

Will importing an MBOX file delete the original file?

No. Importing creates a copy of the emails in your email program. The original MBOX file stays on your computer unchanged. You can delete it once you have confirmed the import worked, or keep it as a backup.

What if the MBOX file has no extension?

Some MBOX files are saved without a file extension. Right-click the file, select "Rename", and add .mbox to the end of the name. Then try importing it again. Your email program should recognize it.

Can I open multiple MBOX files at once?

Most email programs import one MBOX file at a time. If you have many files, you will need to repeat the import process for each one. Thunderbird is usually the fastest for this because the import dialog remembers your last location.

What is the difference between MBOX and PST files?

MBOX is a plain-text format used by Thunderbird, Gmail, and Apple Mail. PST is Outlook's proprietary format. Both hold multiple emails in one file, but they are not compatible. You must convert between them by importing one format and exporting as the other.