How to Convert PST to MBOX and Move Outlook Mail to Thunderbird

Thunderbird's built-in Outlook import, and its limits

Thunderbird's Import tool (Tools > Import, or the import wizard on first run) can pull mail from Outlook. It reads the data through the Outlook installed on the same Windows PC, which brings some limits:

• Outlook must be installed and set up on that PC.
• It reads the mail profile Outlook is using, so a loose PST from a backup drive or an old computer is awkward to get at.
• Large mailboxes can import slowly or stop partway, and you won't always be told which folders were skipped.

If Outlook and Thunderbird are on the same PC and the mailbox is small, try it first. It costs nothing.

Convert PST to MBOX with a converter

Magic Soft PST Converter writes MBOX files straight from the PST. Outlook doesn't have to be installed, so it handles PSTs copied from other machines, and it can process several PSTs in one run.

The duplicate filter is worth turning on if the PST was ever imported twice. It compares sender, recipient, subject and body and skips repeats.

Import the MBOX files into Thunderbird

There are two ways. The add-on route is easier for most people.

With ImportExportTools NG (recommended):

1. In Thunderbird, open Add-ons and Themes and install ImportExportTools NG.
2. Right-click Local Folders and choose ImportExportTools NG > Import mbox file.
3. Choose the option to import a whole directory with subdirectories, and select the export folder. The structure comes in as it was.

By copying files (no add-on): close Thunderbird, then copy the MBOX files into your profile's Mail\Local Folders\ folder (find it via Help > Troubleshooting Information > Profile Folder). Restart Thunderbird and it builds the indexes. Leave off the .mbox extension so Thunderbird recognises the files as folders.

Import the MBOX into Apple Mail

1. Copy the exported MBOX files to the Mac.
2. In Apple Mail, choose File > Import Mailboxes.
3. Select Files in mbox format and point it at the folder.
4. The mail lands in an Import mailbox under On My Mac. Drag folders where you want them.

After the move: a quick checklist

• Compare folder counts between Outlook and Thunderbird for two or three big folders.
• Open a few emails with attachments and make sure they open.
• Contacts and calendars aren't in MBOX. Export them from the PST to VCF and ICS: see exporting PST contacts to vCard.
• Keep the original PST until you've used the new setup for a few weeks.

Which method should you choose?

Summary

If Outlook is still installed and the mailbox is small, try Thunderbird's own importer. For loose PST files, large archives or Apple Mail, convert to MBOX and import the folder tree. Going the other way? See how to convert MBOX to PST.