OLM to PST: the routes that actually work

First, the straight answer

Outlook for Windows keeps mail in .pst files and can import a .pst. Outlook for Mac exports .olm. Microsoft offers nothing that turns one into the other, and Outlook for Windows can’t import .mbox or .eml files in bulk either. Mailunwrap reads .olm archives and exports them as .mbox, .eml and PDF. It doesn’t make .pst files, and this page won’t pretend otherwise.

Route 1: let the mail server do it

If the Mac’s Outlook was connected to Microsoft 365, Exchange, Outlook.com or any IMAP account, the mail is probably still on that server. Sign in to the same account in Outlook for Windows and it downloads. This only misses mail kept in “On My Computer” folders on the Mac, or mail that was deleted from the server. If you also want a .pst, classic Outlook for Windows can export one: File > Open & Export > Import/Export > Export to a file.

Route 2: .olm to .mbox, then through an IMAP account

This is the free route for an archive with no server behind it, such as an old export or local folders.

1. Open the .olm here and export it as .mbox (part of the £6 unlock). You get one .mbox file per folder.
2. Install Thunderbird (free) and import the .mbox files. The free ImportExportTools NG add-on does this; recent Thunderbird versions can also import some mailbox files from their own Import tool.
3. Add an IMAP mail account to Thunderbird, for example an Outlook.com or Microsoft 365 mailbox, and drag the imported folders into it. Thunderbird uploads them to the server.
4. Add the same account to Outlook for Windows. The folders appear there. If you need a .pst file, export one from classic Outlook as in route 1.

It takes a while for a big archive, because every message is uploaded and downloaded again, but it costs nothing and keeps folders, dates and attachments.

Route 3: individual .eml files

Outlook for Windows opens a single .eml file when you double-click it, and you can then move it to a folder. Some versions of classic Outlook also accept .eml files dragged from File Explorer into a mail folder. How well that works varies, so try a few before relying on it for thousands.

Route 4: a paid converter

Several desktop programs for Windows convert .olm straight to .pst. Most are paid, and the free trials usually stop after 25 items per folder or so. If you need a .pst on its own with no account involved, one of these is the direct way; check the trial’s limits before buying.

Contacts and calendar

Outlook for Windows imports contacts from a CSV file and calendars from .ics, both through File > Open & Export > Import/Export. Mailunwrap’s export includes a contacts CSV with Outlook’s own column names, one vCard per contact, and an .ics calendar, when the archive has them.