Written by Jennifer Walsh. Reviewed for technical accuracy by Shubham Dixit, Independent Expert in Email Forensics and Data File Conversion. Updated 18 September 2026.
Shubham is an independent external reviewer and not an employee of PCDOTS.
Quick answer. Outlook stores mail in PST, and MBOX is the open mailbox file that Thunderbird and Apple Mail use. Outlook has no built-in MBOX export, so you convert the PST with a free tool like readpst, or bring the mail into Thunderbird and export it as MBOX. A converter does it in bulk without Outlook. MBOX holds your emails, not contacts or calendars.
On this page
- Why won’t Outlook export to MBOX on its own?
- How do you export Outlook to MBOX for free?
- What does the MBOX keep, and what doesn’t it?
- How do you export a PST to MBOX in bulk without Outlook?
- How do you open the MBOX in Thunderbird or Apple Mail?
- Which method should you use?
- Frequently asked questions
Why won’t Outlook export to MBOX on its own?
Outlook stores mail in a PST file, and it only exports to PST or CSV. There’s no MBOX option in Outlook, so you can’t save straight to MBOX from the app.
MBOX is the open mailbox format used by Thunderbird, Apple Mail, Postbox and Eudora. To move Outlook mail into one of those, or to keep a portable archive, you convert the PST to MBOX with a free tool or a bridge.
One thing to set straight, MBOX holds email messages with their attachments, not your contacts or calendar. Those live in vCard and ICS files, so an Outlook to MBOX export is about your mail.
Outlook has no MBOX save, so readpst or Thunderbird makes the .mbox.
“Two facts save people a lot of time here. Outlook has no MBOX export, it only writes PST or CSV. Thunderbird can’t open a PST on its own either. So the bridge is a converter. My free go-to is readpst from the libpst project, one command turns a PST into MBOX files on Windows, Mac or Linux, no Outlook needed. The other thing worth knowing, MBOX is a mail format, so it carries your messages and attachments but not your contacts or calendar. For a big or locked PST, a dedicated converter that reads the file directly is the steady choice.” Shubham Dixit, Email Migration reviewer (draft, pending approval)
How do you export Outlook to MBOX for free?
You export Outlook to MBOX for free with readpst, an open-source command-line tool from the libpst project. It converts a .pst to .mbox directly, with no Outlook, on Windows, macOS or Linux.
Here are the steps.
- Install libpst, which provides the readpst command. On a Mac run
brew install libpst, and on Ubuntu runapt install pst-utils. - Run
readpst -o output-folder mailbox.pstagainst your PST file. - readpst writes one .mbox file per folder into the output folder.
- Open the .mbox in Apple Mail, or import it into Thunderbird with the free ImportExportTools NG add-on.
When I have a Linux box handy, readpst is my go-to, one command turns a PST into MBOX. If you’d rather stay in a window, the Thunderbird bridge works too. Thunderbird can’t read a PST on its own, so you import the mail through its Tools then Import option while Outlook is installed, then export the folder as MBOX with ImportExportTools NG.
readpst turns the PST into MBOX, then Thunderbird or Apple Mail opens it.
What does the MBOX keep, and what doesn’t it?
An MBOX is a mail file, so it keeps the message and drops anything that isn’t mail. Knowing this avoids a wasted export.
In an MBOX export
- Keeps. Sender, recipient, date, subject, the message body, attachments and the folder structure.
- Drops. Contacts and calendar entries, because MBOX is a mail-only format. Export those to vCard and ICS instead.
How do you export a PST to MBOX in bulk without Outlook?
You export a PST to MBOX in bulk without Outlook by using a converter that reads the file directly. It opens the .pst or .ost and writes MBOX files, so there’s no command line and no Outlook to configure.
PCDOTS PST Converter loads one or many PST files and exports them to MBOX for Thunderbird, Apple Mail and other clients. It keeps the folder structure and attachments, runs on Windows without Outlook. It handles large PST files. The free trial exports a sample first. Follow these four steps.
- Install and run PCDOTS PST Converter, then open the menu.
- Add your PST files or an entire folder.
- Open Export and select MBOX.
- Select a destination and save, then open the MBOX in Thunderbird or Apple Mail.
The tool route, PST files exported to MBOX for Thunderbird or Apple Mail.
Here are the same four steps with the screens.
Step 1. Install and run PCDOTS PST Converter.
Step 2. Add your Outlook data or PST files.
Step 3. Open Export and select MBOX.
Step 4. Browse to a destination and save.
Related reading, our guides to extract email addresses from an MBOX file and import Yahoo Mail to Thunderbird. To read the result, the free MBOX viewer opens a .mbox without any client.
How do you open the MBOX in Thunderbird or Apple Mail?
Once you have the .mbox, loading it takes a minute. Use the import option rather than copying the file, so the client reads every message cleanly.
- Thunderbird. Right-click Local Folders, open ImportExportTools NG, then Import mbox files, then select the .mbox.
- Apple Mail. Open Mail, click File, then Import Mailboxes, then Files in mbox format, then choose the folder.
If Thunderbird shows an empty folder after a copy, that’s a newline or encoding mismatch between systems. Importing through ImportExportTools NG fixes it, since it rewrites the MBOX cleanly.
Import the .mbox rather than copying it, so every message shows up.
Which method should you use?
Use readpst for a free command-line run, and a converter for a big PST or a hands-off window.
| Method | Best for | Good to know |
|---|---|---|
| readpst (libpst) | A free direct run | Command line, no Outlook |
| Thunderbird bridge | Staying in a window | Free, import then export MBOX |
| PST Converter | A big PST, no code | Windows, bulk, folders kept |
Key takeaways
- Outlook has no built-in MBOX export, so you convert the PST with a free tool or a bridge.
- The free readpst command turns a PST into MBOX files directly, with no Outlook.
- MBOX holds mail and attachments only, not contacts or calendar entries.
- A converter reads a big PST directly and exports MBOX in bulk for Thunderbird and Apple Mail.
Frequently asked questions
Can Outlook export to MBOX directly?
No. Outlook exports only to PST or CSV, with no MBOX option. You convert the PST to MBOX with readpst, a Thunderbird bridge or a converter.
How do I export Outlook to MBOX for free?
Run the free readpst command from the libpst project against your .pst file, and it writes .mbox files with no Outlook. Then open them in Thunderbird or Apple Mail.
Does MBOX include my contacts and calendar?
No. MBOX is a mail-only format, so it holds emails and attachments. Contacts go to vCard files and calendar entries go to ICS files.
Can I export a PST to MBOX without Outlook installed?
Yes. readpst and a desktop converter both read the PST file directly, so Outlook does not need to be installed.
Will the folder structure and attachments be kept?
Yes. readpst writes one MBOX per folder, and a good converter keeps the folder hierarchy and the attachments inside every message.
Which apps open an MBOX file?
Thunderbird, Apple Mail, Postbox, Eudora and other open-source clients read MBOX. A free MBOX viewer opens one without any mail client.
So where is your Outlook mail headed?
Exporting Outlook to MBOX starts with one fact, Outlook won’t do it alone, so you reach for a free tool or a converter. The free readpst command turns a PST into MBOX in one line, and a converter reads a big PST directly and writes the MBOX files without Outlook. Every route gives you an MBOX that Thunderbird and Apple Mail open, holding your mail and attachments. So where is your Outlook mail headed, into Thunderbird by hand, or a batch of PST files in one pass?
