When you run a migration batch job with multiple user accounts it completes for some users and fails for others. The migration batch job has successfully migrated 3/5 of the user mailbox to Office 365, but I still have to get the other mailboxes up to Office 365. When I tried re-running the same migration job the same mailboxes failed again. I then tried to create a new migration batch job for each of the failed mailboxes, however that failed as you cannot have the same mailbox referenced in the same batch job at the same time.
From what I could tell there is no way from inside the GUI to remove migration users from a batch job, and if you are like me and have successful syncs within the same job you probably don’t want to delete the job, and if you are not at the point in which you want to “finalise” the migration job you must somehow remove the failed users from this batch job.
This can only be done using the Exchange Online PowerShell cmdlets. Firstly, create a session to Office 365 and then Exchange Online. From there you can run the following command to view and remove migration users.
Get-MigrationUser –Identity firstname.lastname@example.org | Remove-MigrationUser
When you return to the GUI the users will have been removed from the migration batch and you will be free to create new migration batches to get the mailboxes ingested into Office 365.
It should be noted that you cannot actually complete (or finalise) a migration batch job if there are failed mailboxes referenced in the job. The option does not appear inside the GUI until all mailboxes in that job are “synced” successfully.