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OLMExport

What is an .olm file?

.olm stands for Outlook for Mac archive. Outlook for Mac writes one when you use Tools → Export, and it is the only thing that writes one. It holds mail, attachments, contacts and calendar items in a single file, and unlike your live mailbox it is a snapshot: whatever was there on the day it was made.

What's inside one

A .olm is a ZIP container. Rename it to .zip and unzip it and you find Accounts/ and Local/ trees, a Categories.xml at the root, and per-folder directories named com.microsoft.__Messages holding files like message_00012.xml. Each of those is one message, written as XML with Microsoft's OPF element names, OPFMessageCopySubject, OPFMessageCopySenderAddress, OPFMessageCopyHTMLBody. Attachments are ordinary files in a sibling com.microsoft.__Attachments directory, pointed at from the message by OPFAttachmentURL. Contacts and calendar entries have their own directories, com.microsoft.__Contacts and com.microsoft.__Calendar, with one XML document per item.

How to open one

  1. Read it here: drop the file on the viewer and the folder tree appears. Nothing is uploaded.
  2. Or convert it to a format your own software takes: MBOX for Apple Mail and Thunderbird, EML for individual messages, PDF for a record copy, CSV for a spreadsheet, vCard for contacts, ICS for the calendar.
  3. Or import it back into Outlook for Mac, which is what the format was designed for: File → Import → Outlook for Mac archive file (.olm).

What an .olm holds

  • Mail with attachments, in the folder structure it had in Outlook
  • Contacts, if they were ticked at export time
  • Calendar items, if they were ticked
  • Tasks and notes, in Outlook's own XML shapes
  • Categories, in Categories.xml at the root of the archive

Things worth knowing

  • Microsoft has never published the format. Everything known about it comes from reading archives, which is why every converter, including this one, describes contacts and calendar handling as best-effort.
  • Timestamps inside are UTC, written without the Z suffix that would say so. A reader that assumes local time shifts every date in the archive by its own offset. It is the single most common fault in OLM conversions.
  • .olm is not .pst. PST is Outlook for Windows' binary database; OLM is a ZIP of XML. Neither program reads the other's file.
  • .olm is not .ost either. OST is an offline cache of a server mailbox, and also Windows-only.
  • An .olm is not encrypted or password-protected. Anyone with the file can read it, which is worth remembering before emailing one to a colleague.

Questions

What opens an .olm file?
Outlook for Mac imports one. Nothing else on macOS or Windows opens it natively, which is why converters exist. The viewer on this site reads it in the browser without installing anything.
Is an .olm the same as a Mac Outlook profile?
No. The live profile is a folder of databases inside ~/Library/Group Containers/, managed by Outlook. The .olm is a self-contained export you made on purpose.
Can I recover deleted mail from an .olm?
Only what was in Outlook when the archive was made, including anything still sitting in Deleted Items at that moment. There is no undelete inside the file.
Why is my .olm so much smaller than my mailbox?
Either not every item type was ticked at export, or Outlook had not downloaded the older server mail. Check the sync range in the account settings and export again.
Can I edit an .olm?
In principle, since it is a ZIP of XML. In practice, do not: Outlook is fussy on import, and an edited archive is no longer a faithful copy of anything. Convert it instead and edit the output.

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