How to Open MBOX Files on MacOS or Windows

What this email-friendly file is and how to get it open.

Rae Hodge Former senior editor
Rae Hodge was a senior editor at CNET. She led CNET's coverage of privacy and cybersecurity tools from July 2019 to January 2023. As a data-driven investigative journalist on the software and services team, she reviewed VPNs, password managers, antivirus software, anti-surveillance methods and ethics in tech. Prior to joining CNET in 2019, Rae spent nearly a decade covering politics and protests for the AP, NPR, the BBC and other local and international outlets.
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If you're looking to transfer your old emails to a new email address, or if you've ever needed to send someone a mile-long email thread -- MBOX files can be an easy, flexible solution. MBOX files can be opened on MacOS, iPhone, Windows and Android. 

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What exactly are MBOX files? 

MBOX files are a container for multiple, compressed email files. The simple format is an excellent organizational tool for exporting and delivering a large group of emails -- all while keeping those emails' attachments. MBOX files are a convenient and flexible file format that can be opened in any text editor -- including Microsoft Notepad, Apple TextEdit or GitHub Atom. They can also be opened in through email client applications on both MacOS and Windows. 

Here's how to open MBOX files with Mozilla Thunderbird, Apple Mail, and Outlook.

Read more: How to Secure Your Email as Cybersecurity Concerns Grow

Open MBOX files in Mozilla Thunderbird

1. From inside the Thunderbird app, select Menu and choose Account Settings

2. When the Account Settings screen opens, click Local Folders on the left. 

3. Under the Message Storage header, select the Browse button on the bottom-right corner.

4.  In the new pane that opens, navigate to the folder where you've previously saved your MBOX file and click Select Folder. When Thunderbird asks you for a restart, oblige it. 

When Thunderbird re-opens, your MBOX file will appear in your inbox's Local Folders section and you'll be able to browse its full contents and attachments. 

Open MBOX files in Apple Mail 

1. On your Mac, open the Mail application.

2. In the File menu, select Import Mailboxes

3. In the new pane that appears, select Files in mbox format from the option list, and hit Continue.

4. In the next window that appears, navigate to your previously saved MBOX file, select it and hit Choose

5. In a new window, Apple Mail will confirm where you can find the newly imported MBOX file, and you can select Done to close the window. 

How to open MBOX files in Outlook 

Outlook's version of the MBOX file is the PST file. So for Outlook to read your imported file, you'll first need to convert it to PST. We advise a bit of caution if you're searching for an easier way around this common inconvenience. Less-than-reputable tools abound which promise to easily import your MBOX email contents.

Luckily, Microsoft's own suite of apps includes a helper app for this, called Convert To Outlook. Eliminate potential privacy risks and stick to the genuine article.