Move mail between Thunderbird and Outlook

Thunderbird stores mail as MBOX files; Outlook uses PST. How to find the files and convert them, in both directions, without uploading your mail anywhere.

Updated 27 October 20266 min read

Thunderbird to Outlook

Thunderbird keeps each folder as an MBOX file inside its profile. To bring the mail into Outlook you turn those files into a PST.

1. Find the Thunderbird folders

In Thunderbird open Help › Troubleshooting Information and click Open Folder next to Profile Folder. Your mail is under Mail (POP and local folders) or ImapMail (IMAP accounts). Each mail folder is a file without an extension, named like the folder (Inbox, Sent), next to a .msf index file you can ignore.

Close Thunderbird and copy the folder you need somewhere convenient.

2. Convert to PST

Open MBOX to PST and drop the files or the whole folder. Files without an extension are recognised as MBOX when they start like one. Thunderbird keeps subfolders in .sbd directories; they are imported as folders of the same name. Preview the import for free, then create the PST.

3. Open it in Outlook

In classic Outlook: File › Open & Export › Open Outlook Data File to open it as an extra set of folders, or Import/Export › Import from another program or file › Outlook Data File (.pst) to copy the mail into your mailbox.

Outlook to Thunderbird

1. Find the PST

See where is my PST file. For a work or Microsoft 365 mailbox that exists only as an .ost, convert it with OST to PST first.

2. Convert to MBOX

Open PST to MBOX, choose the PST and convert. You get a ZIP with one .mbox file per folder, in your folder structure. Unzip it.

3. Import into Thunderbird

Thunderbird has no built-in MBOX import; the free add-on ImportExportTools NG adds it. After installing it, right-click Local Folders › ImportExportTools NG › Import mbox file, and choose the files.

What comes across

Subjects, senders and recipients, dates, plain-text and HTML bodies and attachments move in both directions. Contacts and calendars are separate: export them from one program as vCard and iCalendar files and import them in the other.

Frequently asked

Is my mail uploaded during conversion? No. The conversion runs in your browser on your computer.

Can I move only some folders? Yes: pick only the MBOX files you want, or delete folders from the result before importing.

MBOX to PSTGmail Takeout and Thunderbird to Outlook. Free preview, nothing uploaded.
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