We're reviewing several migration options because our company still has a significant amount of Outlook data stored in PST files instead of Exchange Online. Over the years, employees created personal archives to manage mailbox limits, and now we're left with hundreds of PST files spread across laptops, desktops, and network shares. Before completing our Microsoft 365 rollout, we need to consolidate all of this data into user mailboxes without losing important business information.

The biggest challenge is finding an efficient way to import PST to Office 365 while preserving the original folder hierarchy, attachments, categories, timestamps, and other mailbox properties. Manual imports might work for a few users, but they don't seem practical when dealing with hundreds of archives of different sizes. We're also looking for features like batch processing, selective migration, preview capabilities, migration reports, and duplicate detection to simplify validation after each migration phase.

During my research, I came across the DRS Softech PST File Converter while comparing enterprise migration utilities. From the documentation, it appears to support direct Office 365 migration, multiple export formats, advanced filtering, and large PST processing. However, product specifications don't always reflect real-world performance, so I'd rather hear feedback from administrators who've actually completed enterprise PST migration projects.

One question we're still discussing internally is whether it's better to import Outlook PST to Office 365 before moving users to Microsoft 365 or after their primary mailbox has already been migrated. Both approaches seem reasonable depending on mailbox size and project timelines, but I'm interested in learning which workflow reduced user disruption and made post-migration validation easier.

If you've completed a large Outlook archive migration recently, what would you recommend? Were there any lessons learned regarding oversized PST files, damaged archives, duplicate emails, or migration reporting that helped make the overall project more successful?