We're moving our team from Outlook for Mac to Microsoft 365, and I've been researching the most reliable way to convert an OLM (Mac Outlook) file before importing it into Office 365. My biggest concern is preserving mailbox data exactly as it appears in Outlook, especially since some users have years of archived emails.

I recently evaluated MacSonik OLM Converter on macOS, and it seems designed specifically for this type of migration. The software reads OLM files directly without requiring Outlook for Mac, then converts them into Outlook-compatible PST files. Before exporting, it lets you preview emails, contacts, calendars, tasks, and mailbox folders, which is useful for confirming that the correct data will be migrated.

One thing I liked was how well it maintained mailbox integrity. It preserved folder hierarchy, sender and recipient details, CC/BCC fields, timestamps, Internet headers, HTML formatting, inline images, signatures, hyperlinks, and attachments. After importing the PST into Microsoft 365, the mailbox organization remained intact.

For larger migrations, features like batch OLM conversion, duplicate email detection, attachment management, Unicode support, and the PST Split option were especially helpful. Since the entire process runs offline on the Mac, there was no need to upload sensitive mailbox data to a cloud service during conversion.

The latest Version 26.6 also mentions faster processing, improved support for OLM files larger than 50GB, better compatibility with macOS Sequoia and Sonoma, enhanced Microsoft 365 authentication, and improved handling of minimally corrupted OLM files.

Has anyone compared converting OLM to PST versus using a direct Office 365 migration tool? Which method gave you the most reliable results with large Mac Outlook mailboxes?
Try - https://www.macsonik.com/olm/converter/