A migration that got run twice left every mailbox in our Microsoft 365 tenant with doubled mail. 30 users. Support says restore from backup, which we do not have from before the mess. How do we dedupe tenant wide?
How to remove duplicate emails in Office 365?
Solved Cloud & Migration
BA
Barry Allen January 21, 2021
2 replies
5,120 views
Reviewed by moderators
Twice-run migrations are the classic cause and there is no native fix. SysTools Office 365 Duplicate Remover works tenant wide with admin credentials: select all 30 mailboxes and it matches duplicates per mailbox on message id and content fields. Extras get routed to Deleted Items or a quarantine folder for review.
Run one mailbox first and review the quarantine before unleashing it on all 30. Trust, then verify, then batch.
Pilot mailbox checked clean, then all 30 overnight. Roughly 400,000 duplicates removed. Solved.