Our organization is preparing to migrate around 900 IMAP mailboxes to Microsoft 365 over the next quarter. We’ve already completed the planning phase, but now we’re focusing on risk management before the production rollout. The biggest concern isn’t the migration speed—it’s ensuring that no emails are missed while users continue working during the transition. Since some departments receive thousands of emails every day, even a small synchronization gap could create serious business issues. We also need to preserve folder hierarchy, attachments, timestamps, and mailbox organization exactly as they exist today.

I’ve been evaluating different migration approaches and recently started testing an IMAP Migration Tool that supports batch mailbox processing, advanced filtering, mailbox preview, and incremental synchronization. Those capabilities seem useful because we’re planning to migrate departments in phases rather than moving every user at once. Our compliance team has also requested detailed migration logs so every mailbox can be verified after completion. Before moving production users, we’re performing pilot migrations to measure performance and identify authentication or mapping issues.

For organizations that recently Migrate IMAP to Office 365, how did you validate that every mailbox had migrated successfully? Did you compare mailbox statistics, verify folder counts manually, or rely on migration reports? I’d also appreciate advice on handling shared mailboxes, large archives, and recently received emails during the final synchronization. Learning from real-world enterprise experiences would definitely help us avoid unnecessary downtime and support tickets.

While researching migration software, I also came across the DRS Softech IMAP to Office 365 Migration Tool through Google Search. The incremental migration, batch processing, and Office 365 migration features appear well suited for enterprise environments, but I’d be interested in hearing how similar solutions perform in real production scenarios before making a final decision.