MSF to PST — move Thunderbird mail to Outlook
An .msf file holds no mail: it is Thunderbird’s index. Open the file next to it, or the whole profile folder, and save the messages as a .pst for Outlook. In your browser, nothing uploaded.
About this conversion
Searching for an MSF to PST converter is the natural thing to do, because .msf files are what you see in a Thunderbird profile. But an .msf holds no messages at all: it is the index Thunderbird builds so that a folder opens quickly. The mail is in the file right next to it, with the same name and no extension — “Inbox” beside “Inbox.msf”. That file is an mbox, and this page turns it into a .pst that Outlook opens or imports. If you drop an .msf here by mistake, you are told which file to open instead.
Where the mail file is
In Thunderbird, open Help › Troubleshooting Information and click Open Folder next to Profile Folder. Mail from a POP account or Local Folders is under Mail, and mail from an IMAP account is under ImapMail, in a folder named after the account or server. Each mail folder is a pair: “Inbox” and “Inbox.msf”, “Sent” and “Sent.msf”. Subfolders sit in a folder ending in .sbd.
Close Thunderbird before you copy or open these files, so that nothing is writing to them at that moment.
If the file is missing or small
For an IMAP account, Thunderbird keeps complete messages only for folders it syncs for offline use, so the local file can hold headers only or be nearly empty. Turn on offline sync for that account in Account Settings › Synchronization & Storage, let it download the mail, then convert the file.
Just want to look inside it?
The same tool without converting anything: open a .mbox file and read it.
You are not locked into PST
The file is parsed once and stays open, so the format is picked at the end rather than the beginning: the same archive can leave here as CSV, XLSX, ZIP, EML, PDF, HTML, TXT or JSON. Before that you can search it by subject or address, filter by year, sender and attachment type, mark the duplicates and look through the archive overview.
Questions
- Can I convert the .msf file itself?
- No, and no converter can: the file holds an index of the folder, not the text of the messages or their attachments. If the mail file is gone, the .msf cannot bring it back.
- Can I select the whole profile folder?
- Yes. Choose the folder and the mail files are read; .msf files and Thunderbird’s own settings files are skipped, and you see which ones. All the messages then land in one .pst. To keep Inbox and Sent apart in Outlook, convert each file on its own.
- Will messages I deleted in Thunderbird come back?
- No. Thunderbird only marks a deleted message and leaves it in the file until the folder is compacted, so it can still be in there. Messages marked this way are hidden and left out of the .pst, and you are told how many. Tick “show deleted” if you want one of them back. A copy may also be in the Trash file, which counts as its own folder if you open it.
- How do I get it into Outlook?
- In classic Outlook for Windows, use File › Open & Export › Open Outlook Data File, or Import/Export to merge it into your mailbox. The new Outlook for Windows opens .pst files only with a Microsoft 365 subscription.