Written by Jennifer Walsh. Reviewed for technical accuracy by Shubham Dixit, Independent Expert in Email Forensics and Data File Conversion.
Shubham is an independent external reviewer and not an employee of PCDOTS.
Quick answer. Outlook cannot open an MBOX file on its own, so importing one means getting the mail into a PST that Outlook reads. If you have Thunderbird, you can bridge the mail across for free. Or convert the MBOX files to PST with a converter and import that into Outlook 2021, 2019 or Microsoft 365.
On this page
Why Outlook will not open an MBOX file?
An MBOX file holds a whole mailbox in one file, and it is the format that Thunderbird, Apple Mail and Eudora use. Outlook is the odd one out. It stores mail in a PST file and has no option anywhere to open or import an MBOX directly. That single fact shapes every method below. To import MBOX files to Outlook you first have to get the mail into a PST, the format Outlook understands, and then bring that PST into Outlook. Once you see it as MBOX to PST to Outlook, the rest is just picking how you make the PST.
The mail has to pass through a PST, the only mailbox format Outlook opens.
Which method fits your situation?
There are two real ways to make that PST, plus a quick option if you only want to read the file. If Thunderbird is on your computer, you can move the mail into Outlook for free by syncing it through an account. If you would rather not touch Thunderbird, or you have many files or a large mailbox, a converter turns the MBOX straight into a PST. And if you just need to look inside the MBOX, a free viewer opens it without importing anything. Pick the route that matches your case.
A free bridge through Thunderbird, a converter for bulk, or a free viewer just to read.
How to import MBOX to Outlook free with Thunderbird?
If you already use Thunderbird, or you are happy to install it, you can move MBOX mail into Outlook without paying for anything. Thunderbird acts as the bridge, and an email account you can reach from both apps carries the mail across.
Step 1. In Thunderbird, install the ImportExportTools NG add-on, then use it to import your MBOX file into a local folder.
Step 2. Add an email account to Thunderbird over IMAP, the same account you will open in Outlook, so it appears in both apps.
Step 3. Drag the imported messages onto a folder under that IMAP account. Thunderbird uploads them to the mail server.
Step 4. Open the same account in Outlook and let it download the mail. Your MBOX messages now sit in Outlook.
“The Thunderbird bridge is a real free option, but two things bite on bigger mailboxes. Nested folders can flatten when they sync, and the mail server throttles IMAP, so a large move crawls or stalls. For a few folders it is fine. For a deep folder tree or tens of thousands of messages, converting straight to a PST keeps the structure and finishes cleanly.” Shubham Dixit, Email Migration reviewer (draft, pending approval)
How to convert MBOX to PST and import it?
When you do not want the Thunderbird detour, or you have several MBOX files or a heavy mailbox, the direct route is to convert the MBOX into a PST and import that. A converter reads the MBOX files and writes a standard PST, keeping the folder hierarchy and attachments in place. The PCDOTS MBOX Converter does this in bulk, turning a folder of MBOX files into PST in one run, and it works with MBOX from any of the common clients. There is a free trial so you can check it on your files before buying. If you only want to read an MBOX rather than import it, the free MBOX Viewer opens it without converting anything.
Converting MBOX to a PST that you then import into Outlook.
Here are the steps with the screens.
Step 1. Launch the converter and choose the MBOX file and folder option.
Step 2. Select the MBOX files you want to import.
Step 3. The converter loads your files and folders for preview.
Step 4. Pick PST as the export type, set the destination, and click Save to start.
How to import the PST into Outlook 2021, 2019 and 365?
However you produced the PST, the last step is the same and it works the same across versions. In Outlook, go to File, then Open and Export, then Open Outlook Data File, and select the PST to see its folders in your list. To merge the mail into your existing folders instead, choose Import and Export, then Import from another program or file, and pick the PST. Outlook 2021, 2019, 2016 and the Microsoft 365 desktop app all read a standard PST without any extra setup, so the same steps cover almost any Windows machine.
The methods compared
The common ways to import MBOX into Outlook, side by side.
| Method | Best for | Watch out for |
|---|---|---|
| Thunderbird bridge | A modest mailbox, free, with Thunderbird | Slow on big mailboxes, folders can flatten |
| MBOX to PST converter | Bulk, no Thunderbird, keeps folders | Free to try, full version is paid |
| Free MBOX viewer | Reading the file, no import | Views only, does not move mail in |
Frequently Asked Questions
Can Outlook open an MBOX file directly?
No. Outlook has no option to open or import MBOX. You move the mail into a PST first, then open or import that PST in Outlook.
How do I import MBOX to Outlook for free?
If you have Thunderbird, import the MBOX into it, add an IMAP account, drag the mail to sync it to the server, then open the same account in Outlook so the mail downloads.
How do I import MBOX to Outlook without Thunderbird?
Use a converter to turn the MBOX files into a PST, then open or import that PST in Outlook. This also handles many files at once.
Does importing MBOX keep my folders and attachments?
A converter keeps the folder hierarchy and attachments in the PST. The Thunderbird bridge can flatten nested folders on large mailboxes.
Will this work in Outlook 2021, 2019 and Microsoft 365?
Yes. The methods produce a standard PST, and every recent Outlook version, including the Microsoft 365 desktop app, opens a PST without extra setup.
Can I import several MBOX files at once?
A converter supports bulk import of many MBOX files in one run. The Thunderbird bridge moves one folder at a time.
Old mailbox, new home in Outlook
Outlook keeping its distance from MBOX is the whole challenge, and once you know the mail has to land in a PST, the path is clear. With Thunderbird on hand you can sync the messages across for nothing, which suits a smaller mailbox. For many files, a deep folder tree or a large account, converting straight to a PST keeps everything in order and saves the fiddly steps. Either way, import the PST into Outlook and your old mailbox is finally somewhere you can search and use every day.
