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File ConvertersAn OLM file is the archive that Outlook for Mac creates when you export a mailbox: email messages, contacts, calendar events, tasks and notes in one file. Outlook for Windows cannot open or import it, because Windows Outlook uses the PST format instead. To read an OLM file on a PC you either import it into Outlook for Mac or convert it to PST, PDF or EML.
What is an OLM file?
Microsoft calls it the Outlook for Mac Data File. You get one by choosing File > Export in Outlook for Mac, ticking the item types you want (mail, contacts, calendar, tasks, notes) and saving the archive. Users create OLM files to back up a mailbox, to move an account to another Mac, or to hand over a former employee’s correspondence.
| Property | OLM file |
|---|---|
| Extension | .olm |
| Developer | Microsoft |
| Created by | Outlook for Mac, File > Export |
| Contains | Mail folders, contacts, calendar, tasks, notes, attachments |
| Structure | Compressed (ZIP-based) archive of XML records and attachment files |
| Opens with | Outlook for Mac (File > Import); OLM converters on Windows |
Internally an OLM file is a compressed archive. Each message, contact or event is stored as an XML record inside folders that mirror the mailbox, with attachments saved as separate files. That structure is what OLM viewers and converters read on Windows, where Outlook itself has no idea what to do with the file.
OLM vs PST vs OST
The three Outlook data formats are not interchangeable. PST is the Windows Outlook archive and the only format Windows Outlook imports. OST is the offline cache of an Exchange or Microsoft 365 mailbox on Windows and is not meant to be moved at all. OLM is the Mac export. If a colleague sends you an OLM file and you work on Windows, you cannot rename it to .pst; the internal structures have nothing in common. Single messages saved from Windows Outlook use the MSG format; OLM has no single-message equivalent.
| OLM | PST | OST | |
|---|---|---|---|
| Platform | Outlook for Mac | Outlook for Windows | Outlook for Windows |
| Purpose | Export / backup | Archive, POP mailbox, export | Offline cache of a server mailbox |
| Importable into Windows Outlook | No | Yes | No |
| Importable into Outlook for Mac | Yes | Yes | No |
How do I open an OLM file?
- On a Mac with Outlook. Open Outlook for Mac, choose File > Import, select Outlook for Mac archive file (.olm), and pick the file. The folders appear under On My Computer. This is the only native way to open an OLM archive.
- On Windows. Windows Outlook cannot import OLM. Use a converter that reads the archive directly and writes the messages out in a format Windows understands: PDF for reading and archiving, EML or MSG for another mail client, or PST for Windows Outlook.
- Without any Outlook. Convert the archive to PDF or HTML and read the messages in a browser or PDF viewer.
How do I convert an OLM file on Windows?
Total Mail Converter Pro reads OLM archives on Windows without Outlook for Mac and converts the messages to PDF, DOC, TXT, HTML, TIFF, RTF or JPEG. It converts the attachments as well, so a message with a DOCX or XLSX attached becomes one PDF with the attachment rendered after the message body. The program keeps the folder tree of the archive, can combine everything into a single PDF, and runs from the command line for unattended jobs. The 30-day trial is free and needs no card or email; a Personal license starts at $129.90.
If the goal is to get the mail back into Windows Outlook rather than into documents, the route is OLM to PST with a dedicated migration tool, then File > Open & Export > Import/Export in Outlook. For single messages, saving them as EML from a converter and dragging them into Thunderbird or Windows Mail works too.
Frequently asked questions
How do I open an OLM file?
Import it into Outlook for Mac with File > Import. On Windows, Outlook does not open OLM files; use Total Mail Converter Pro or another OLM converter to turn the archive into PDF, EML or PST.
Can Outlook for Windows open OLM files?
No. Windows Outlook reads PST and OST only. An OLM archive must be converted to PST before Windows Outlook can import it, or converted to PDF or EML if you only need to read the messages.
Can you convert OLM to PST?
Yes, with third-party OLM to PST migration software on Windows or Mac. Outlook itself offers no direct path. After conversion, import the PST through Outlook’s Import/Export wizard.
What is the OLM file format used for?
Backing up and moving Outlook for Mac data. It stores mail, contacts, calendar items, tasks and notes in one archive that another Outlook for Mac installation can import.
What is the difference between OLM and PST?
Both are Outlook archives, but OLM comes from Outlook for Mac and PST from Outlook for Windows. Their internal structures differ completely, and neither program reads the other’s format without conversion.
