Guides / Open an OLM on Windows

How to open an OLM file on Windows

Updated August 30, 2026

Someone archived their mail on a Mac and sent you the result. Outlook for Windows looks at the .olm file and offers you nothing: no import option, no error worth reading, no way in. This is not a broken file. Windows Outlook has never been able to read the Mac archive format.

What is inside an .olm

Unlike a PST, which is a database, an OLM is a ZIP archive. Rename a copy to .zip, extract it, and you get a folder tree that mirrors the mailbox, with one small XML file per message under paths like Accounts/<account>/.../Messages/message_0001.xml. Older exports put their folders under Local/ instead. Each XML holds the subject, the sender, the recipients, the timestamps and the body. Attachments sit alongside as ordinary files.

That is genuinely good news. Nothing is encrypted, nothing is proprietary beyond the field names, and everything you need is in there in plain text. The problem is purely that no Windows mail client speaks it.

Ask the boring question first

If the Mac account was Microsoft 365, Exchange or IMAP, the mail is still on the server. Add the account in Outlook for Windows and you have all of it, indexed and searchable, without touching the archive. An OLM is usually a copy of something that already exists somewhere better. Only when the account is closed, or the archive holds mail that was deleted from the server, is converting the file the actual job.

The routes that work

Unzip it and read the XML. Free, immediate, needs nothing installed. Copy the file, rename the copy to .zip, and extract. If you want two messages and an attachment, you are done in a minute. If you want two thousand, this is not a plan.
Let a mail server do the conversion. If you can borrow the Mac for an hour, this is the most reliable path there is and it costs nothing. Import the OLM back into Outlook for Mac, add any IMAP account you control, then drag the folders into it. The messages upload. Add the same account in Windows and drag them back down into a local folder. The server is the best format converter you own, because both clients already agree on how to talk to it.
Convert to .eml and drag them in. Outlook for Windows opens .eml files and lets you drop them straight into a mail folder. Anything that turns an OLM into .eml files therefore gets your mail into Outlook. FileQuiet's email archive tool does exactly this in your browser, with nothing uploaded.
Paid converters. They exist, and some are competent. Two cautions: most run on their servers, which means posting a mailbox to a stranger, and the category is full of tools that charge for a preview and then produce a mess. If you use one, test with a small export first and read where the parsing happens.

What will not work

Renaming .olm to .pst. The formats have nothing in common. Outlook will reject the file or report it as corrupt.
Thunderbird. No native OLM support, and no add-on that reliably provides it.
Outlook for Windows import. The importer handles PST and a few legacy formats. OLM has never been on the list.

What survives the trip, and what does not

Message text, sender and recipients, dates, folder structure and attachments come across cleanly in any of the routes above, because they are all stored plainly in the archive. Mac-specific extras travel less well: categories, flags, and some calendar and contact items may be simplified or dropped depending on the tool. If the archive is evidence for a legal matter, keep the original .olm untouched alongside whatever you produce from it.

Reading it without installing anything

FileQuiet's email archive tool opens OLM, PST, OST and MBOX files in your browser tab. The parser is JavaScript running on your machine, so the archive is never uploaded, and you can watch the network tab while it opens to confirm that. Browsing folders, reading messages, searching the whole archive and saving a single message as .eml or PDF are free. A one-time $12 unlocks bulk export: every message as .eml files in a zip, one combined PDF, or a CSV index.

Open an OLM in your browser

Honest limits: the archive is held in browser memory while it is open, so very large files can run a tab out of room. Exported .eml files drag into Outlook, but they arrive as individual messages rather than as a mounted mailbox.

Frequently asked

Can I convert an OLM to a PST for free?

Not with a single command, because no free tool writes the PST format well. The free path that works is to move the mail through an IMAP account, or to convert to .eml files and drop those into an Outlook folder, which puts the messages in your mailbox and lets Outlook build the PST itself.

Is an OLM file encrypted?

No. It is a ZIP archive of XML files. Rename a copy and extract it to see for yourself. That also means an OLM sitting in a shared folder is about as private as a folder of documents, which is worth remembering before emailing one around.

Why does Outlook say the file is not a valid data file?

Because you pointed the PST importer at an OLM, usually after renaming it. The message is accurate: it is not an Outlook data file. Rename it back to .olm and use one of the routes above.

The .olm will not open on the Mac either. Now what?

Try the unzip test first. If the copy will not extract as a ZIP, the file was truncated in transfer, which happens with large archives over email gateways and flaky drives. Ask for it again over a link rather than an attachment. If the extraction works but Outlook still refuses, read it with a tool that walks the XML directly.