Import of data from the local PST files of a Microsoft Outlook profile was not working well in Thunderbird before 2011, when famous Russian developer Mike Kaganski*) re-implemented it in bug 207156. His work was committed here with this changeset. That was in 2011 in Thunderbird 6. Back then, our project leader was working with Mike, mostly doing testing. Mike did a few more tweaks, for example here and here, so the feature was stable that year in Thunderbird 11.
With the advent of JS Mime, a new implementation of MIME processing written in JavaScript, Outlook import broke again in Thunderbird 38 due to threading issues. The fix was made in this bug ready for Thunderbird 60 by our project leader.
(The text below has been corrected on 8th November 2025, the initial information was incorrect.)
It's been working since then, but the advent of Outlook 2013/2016/2019, Office 365 and the modern Outlook app have changed the situation. Here is what is still working to this very day:
| Outlook version | IMAP account with OST and optional PST files | POP account with PST only |
|---|---|---|
| Up to 2010 | ✅ Can import via full MAPI | ✅ Can import via full MAPI |
| 2013, 2016, 2019, O365 (classic desktop) | ✅ Can import via full MAPI; attached PSTs also visible if part of the profile | ❌ Cannot import, PST not exposed to external MAPI clients |
| Modern Outlook app | ❌ Cannot import, no MAPI | ❌ Cannot import, no MAPI |
To import a PST with Outlook 2013/2016/2019 or Outlook 365 installed, add it to an IMAP profile (with OST file) as an additional data file.
This screenshot was taken after a successful import from Outlook 2010:
It is possible that modern versions of Betterbird/Thunderbird have additional bugs, so if there is an issue, we recommend using an older version, for example Thunderbird 12 (we didn't test it). Older versions also give a more informative summary panel that the new kids on the block who took over Thunderbird axed in version 128 (bug 1851608):
If you're using Outlook 2013/2016/2019 or Outlook 365 on a POP account or the modern app, you will see this:
*) Mike is famous for cracking bug 393302, the dreaded MAPI x64 bug, that no one had been able to solve and that prevented Thunderbird from shipping 64-bit binaries. That was back in 2019, and the fix was backported to Thunderbird 60.