Best way to upload archived Outlook PST files into Microsoft 365?
I'm looking for advice from anyone who's migrated old Outlook archives into Microsoft 365. We recently discovered hundreds of PST files stored across employee systems, and management wants everything consolidated into Office 365 so users can access their historical emails from anywhere.
Initially, I assumed Outlook would simply import the files into Microsoft 365, but after reading Microsoft's documentation I realized the official process involves Azure Storage uploads, CSV mapping files, Exchange permissions, and Microsoft Purview import jobs. It seems manageable for a few files, but not for dozens or hundreds.
Our biggest priorities are preserving mailbox structure, avoiding duplicate emails, keeping attachments intact, and ensuring that contacts and calendars migrate correctly. Since these archives include compliance-related information, even a small amount of missing data could become a serious issue later.
While searching for alternatives, I found several recommendations to Import PST to Office 365 using specialized migration software instead of manually uploading every archive. That seems like it could save a lot of administrative effort, especially for IT teams handling bulk migrations.
One utility that caught my attention was the DRS Softech PST Converter Tool. According to its documentation, it supports direct Microsoft 365 migration, batch PST processing, mailbox preview, selective migration using filters, duplicate removal, and preservation of folder hierarchy throughout the transfer. Those capabilities sound useful for enterprise migrations where data integrity is essential.
Before making a decision, I'd like to hear real experiences from administrators who've completed similar projects. Did you rely on Microsoft's native method or another migration solution? If you've successfully managed to Upload PST to Office 365 without data loss, I'd appreciate any recommendations, lessons learned, or best practices that helped make the migration smooth and reliable.