During my day to day work as a part of support organization, I work with and help troubleshoot mailbox migrations very often. One type of migrations that we see quite often is IMAP migrations. I want...
Updated Nov 21, 2023
Version 5.0
Blog Post
Mirela_Buru
Microsoft
Microsoftfdosn , sorry for delay.
You probably deal with an orphan sync request. Check if you have a Sync Request still running for the Migration User: Get-SyncRequest -Mailbox <user> . If yes, and you confirm it is for your IMAP migration, then Remove-SyncRequest. This would stop synchronization between source and target mailbox.
Regarding the question for the accepted domain, I am not able to tell you if related or not. I assume your target mailboxes didn't use that accepted domain as Primary SMTP address? Normally, before you start an IMAP migration, you would register your domain, then create mailboxes in Office 365 with that domain, then start migration batch with IMAP, then when in Synced state you switch MX record to point to Office 365, make sure all your email is routed to cloud mailboxes, then you check last synced time and only then delete the IMAP batch. Procedure in detail here: https://docs.microsoft.com/en-us/exchange/mailbox-migration/migrating-imap-mailboxes/migrating-imap-mailboxes