Import OLM to Outlook – Best Methods to Open OLM Files Easily

The first time most people run into this, they assume the file is corrupted. It isn’t. Mac Outlook stores data in OLM format; Windows Outlook uses PST. Same data, different containers — and Microsoft has never built a native converter between them.

There are two ways around it.

Why Windows Outlook Can’t Read OLM Files

Platform	Format	What’s Stored
Mac Outlook	.OLM	Emails, contacts, calendars, tasks, notes
Windows Outlook	.PST	Emails, contacts, calendars, tasks, notes, journals

The formats are fundamentally incompatible wrappers. You can move your emails for free using Gmail as a relay (slow, email-only), or convert the entire mailbox directly to PST using a third-party tool (faster, paid).

Method 1: The Gmail Relay (Free)

Important limitation up front: This method only migrates emails. Contacts, calendars, tasks, and notes do not transfer — IMAP is an email protocol, and there is no workaround for that. If you need anything beyond email, skip to Method 2.

What you need: Your Mac, a Windows PC, a Gmail account, and IMAP enabled in Gmail.

Step 1 — Import the OLM into Mac Outlook

Open Mac Outlook. Go to File > Import, select your OLM file, and let it finish importing.

Step 2 — Add Gmail to Mac Outlook

Go to Tools > Accounts. Before adding the account, make sure IMAP is enabled in Gmail: Gmail Settings > See all settings > Forwarding and POP/IMAP > Enable IMAP. Skipping this step is the most common reason the sync fails.

Step 3 — Drag your folders to Gmail

Under On My Computer in the sidebar, drag your imported folders into your Gmail account. Be patient — a 1 GB mailbox can take around 15 minutes; several gigabytes can take hours. Large mailboxes are prone to timeouts, and Outlook doesn’t always notify you of what failed to sync. You may need to manually verify what was transferred.

Step 4 — Add Gmail to Windows Outlook

On your Windows PC, open Outlook and go to File > Add Account. Sign in with the same Gmail address. It will sync automatically.

Step 5 — Export to PST (optional) 

Go to File > Open & Export > Import/Export > Export to a file > Outlook Data File (.pst). Select the Gmail folders you want and save.

Why this method has serious drawbacks:

• It’s slow. Syncing several gigabytes over IMAP can take hours, with progress that is difficult to track.
• Timeouts are common for mailboxes over 3 GB, and Outlook doesn’t always tell you what didn’t make it.
• Folder structure gets flattened. Nested folders like Clients/Acme/2024/Invoices may be collapsed, losing your organization.
• Attachments over 25 MB are silently dropped. Gmail’s outgoing attachment limit is 25 MB, and because of how Gmail re-encodes files for MIME transmission, the practical limit on file content is closer to 12–13 MB. Files exceeding this are stripped with no notification — you may only notice weeks later when you need a specific attachment.
• Requires your Mac. Once the Mac is gone, this method is unavailable.

Method 2: MacSonik OLM Converter (Paid, Free Trial Available)

This is the recommended approach, especially if you need more than just email.

The converter reads your OLM file and writes a PST — no Gmail account needed, no Mac required after the file is copied over. Everything migrates: emails, contacts, calendars, tasks, notes, and attachments of any size. Folder hierarchy is preserved.

Additional features include batch conversion (useful for multiple accounts), a duplicate filter, and the ability to migrate directly to Google Workspace or Office 365 without creating a PST at all.

How to use it:

1. Download and install MacSonik OLM Converter.
2. Open it, click Select Files, and choose your OLM file.
3. Browse the folder tree and preview your emails to confirm the data loaded correctly.
4. Set File Format to PST.
5. Choose a destination folder.
6. Optionally, use Advanced Filters for date ranges or duplicate removal — worth enabling if the mailbox is disorganized or very large.
7. Click Start Process. Most conversions are complete in a few minutes.

The output is a Unicode PST compatible with Outlook 2016, 2019, 2021, and newer.

Getting it into Windows Outlook: Go to File > Open & Export > Import/Export > Import from another program or file > Outlook Data File (.pst). Select your PST, choose which folders to import, and click Finish. The whole process typically takes around 6 minutes.

Side-by-Side Comparison

Features	Gmail relay	MacSonik
Cost	Free	Paid, free trial
Email	Yes	Yes
Contacts + calendar	No	Yes
Attachment limit	25 GB	None
Folder structure	Gets broken	Stays organized
Need Mac	Yes	No
Batch Converter	No	Yes
Duplicate filter	No	Yes
5 GB mailbox	Hours	Minutes

Common Problems and Fixes

.olm is not an Outlook data file (.pst).

Windows Outlook does not support OLM. You must convert to PST first.

Missing attachments after migration.

This is the Gmail relay silently dropping files over its size limit. MacSonik does not have this limitation.

Contacts didn’t transfer

IMAP only syncs email. You need a dedicated converter for contacts, calendars, and tasks.

The converter appears frozen on a large file

Close background applications. For mailboxes over 10 GB, use the date filter and convert one year at a time.

Duplicate emails after migration

Enable the duplicate filter in MacSonik before starting conversion. If duplicates already exist in Windows Outlook, clean them up via Home > Clean Up > Clean Up Folder.

Frequently Asked Questions

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