Quick answer: You can’t open an OLM file directly in Windows Outlook or New Outlook. The reliable ways to migrate are (1) import it into Outlook for Mac and sync it to a Microsoft 365 mailbox, (2) use an IMAP account as a bridge, or (3) convert OLM to PST and import the result.
If you have an OLM backup from Outlook for Mac and want your emails, contacts and calendars in New Outlook, you’ve probably noticed that nothing happens when you try to open it. That’s expected. This guide explains why and walks through three methods, so you can pick the one that suits your setup.
Why You Can’t Open an OLM File in New Outlook
OLM is the data file format used by Outlook for Mac. OLM files store email messages, calendar data, contacts and application settings, and they are not supported by Outlook for Windows. Windows Outlook relies on PST files instead, so a format conversion or a cloud sync step is needed first.
There’s another catch. In the New Outlook interface, local “On My Computer” folders may not be fully supported or visible. That limits what you can do directly inside New Outlook, and it’s why most successful migrations go through a mailbox account or a PST file.
Before You Start
- Back up your OLM file. Copy it to an external drive or cloud storage.
- Check the file size. This decides which method is practical.
- Know your destination. Is it a Microsoft 365 mailbox, an Outlook.com account or Windows Outlook?
- Have your account credentials ready for the destination mailbox.
Method 1: Import OLM Into Outlook for Mac, Then Sync to Microsoft 365
Use this if you still have access to a Mac and your destination is a Microsoft 365 mailbox.
- Open Outlook for Mac. If you’re on the New Outlook for Mac and the import option is greyed out, switch to Legacy Outlook via Help > Revert to Legacy Outlook.
- Go to File > Import, choose Outlook for Mac archive file (.olm) and click Continue.
- Select your OLM file and click Import.
- In the On My Computer section, create a new folder in your Microsoft 365 mailbox (for example, “Imported History”).
- Drag or move the imported folders into it.
- Wait for the sync to finish, then sign in to New Outlook with the same account. Your data appears there.
Limitation: This needs a Mac with Outlook installed, and large mailboxes can take hours to sync.
Suggested Read: How to Import OLM file to iCloud
Method 2: Use an IMAP Account (Gmail) as a Bridge
If you don’t have a Microsoft 365 mailbox, an IMAP-enabled account can carry your data across.
- Add a Gmail (or other IMAP) account to Outlook for Mac.
- Create a folder under that account and move your OLM folders into it.
- Let the folders sync to the server.
- Add the same account to Outlook on Windows.
- Move the emails from the IMAP folders into your Outlook data file or mailbox.
Limitation: This is slow, and IMAP carries emails well but generally not calendars or contacts. It’s also impractical for large archives because of server storage and sync limits.
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Method 3: Convert OLM to PST Using Stellar OLM to PST Converter Online
If you no longer have a Mac, or you want a faster route that doesn’t depend on syncing, converting the OLM file to PST online is the most direct option. Once you have a PST file, Outlook on Windows can import it through its standard import wizard, and the data then syncs into New Outlook through your account.
Stellar Converter for OLM Online is a browser-based tool that does this in three steps, with nothing to install.
How to use it
- Upload your OLM file at the Stellar OLM to PST online converter.
- Convert the file. The tool tracks progress in real time and preserves your original folder structure.
- Preview and download the PST file. A preview in HTML format lets you check your mailbox data before you download.
Why people choose it
- No Outlook needed. It works even if Outlook isn’t installed on your system.
- Any operating system. It runs in a browser on Windows, Linux or macOS.
- Wide compatibility. It supports OLM files from Outlook for Mac 2021, 2019, 2016 and 2011.
- Folder hierarchy intact. Your mailbox structure stays the same after conversion.
- Secure. Files are uploaded with SSL encryption, and uploaded and converted files are deleted from the servers after 24 hours.
Free vs. Premium
| Free | Premium | |
| Price | $0 | $19.99 |
| File size limit | Up to 100 MB | Up to 5 GB |
| Files | Single file | 5 files |
| Preview | Yes | Yes |
For OLM files larger than 5 GB, Stellar recommends its desktop software, which has no file size limit and offers a free trial.
Import the converted PST
- Open Outlook on Windows and go to File > Open & Export > Import/Export.
- Choose Import from another program or file, then Outlook Data File (.pst).
- Browse to your converted PST and select the destination folder.
- Click Finish, then let your account sync so the data appears in New Outlook.
Which Method Should You Choose?
| Situation | Best method |
| Still have a Mac and a Microsoft 365 account | Method 1 |
| Small archive, mostly emails, no Microsoft 365 | Method 2 |
| No Mac, no Outlook, or you need a fast, preview able result | Method 3 |
| OLM file over 5 GB | Stellar desktop software |
Tips for a Smooth Migration
- Keep the original OLM file until you’ve verified the migrated data.
- Check emails, attachments, contacts and calendar entries after import.
- Migrate in batches if your mailbox is very large.
- Don’t switch off your Mac or internet connection mid-sync.
Conclusion
Migrating an OLM file to New Outlook takes a little planning, because the formats aren’t compatible. If you have a Mac and a Microsoft 365 account, Method 1 works well. If you want a quicker, Mac-free route, converting the file to PST with Stellar’s online converter is the simplest path. You can try the free version on files up to 100 MB first, then upgrade only if you need to.
FAQs
Can I import an OLM file directly into New Outlook?
No. New Outlook doesn’t read OLM files, so you need to sync the data through an account or convert it to PST first.
Can I convert an OLM file to PST for free?
Yes. Stellar’s online tool converts a single OLM file of up to 100 MB for free.
Is it safe to upload my OLM file online?
Stellar uses SSL encryption and deletes uploaded and converted files from its servers after 24 hours. Review its privacy policy before uploading sensitive data.
