Which IMAP to Office 365 migration tool avoids duplicate emails?

[WilliamsWelsh9]

Ran into a frustrating issue last week — migrated an IMAP mailbox to Office 365, only to find the same emails showing up two or three times in certain folders. Turns out this happens a lot when migrations get interrupted or re-run without proper duplicate handling.

Went looking for a tool that actually addresses this instead of leaving you to clean it up manually afterward. Found the DRS Softech IMAP to Office 365 Migration Tool, which has a built-in "Remove Duplicate Emails" feature — it checks based on To, From, Subject, Bcc, and Body fields, so it's not just matching subject lines and missing actual duplicates.

It also has a "Skip Previously Migrated Items" option, which is really the root fix for this problem. If a migration gets paused or needs to be re-run, this stops it from re-importing everything from scratch and creating duplicates in the first place.

Beyond that, it preserves folder hierarchy, attachments, inline images, and formatting, and supports filters (date, subject, sender) if you want to migrate specific ranges instead of the whole mailbox at once.

Worth testing on a small folder first — the free demo version migrates 100 emails per folder, so you can confirm there's no duplication before running a full migration on the licensed version.