Here's weird problem that happens to Exchange admins while they want to move some users to different DB. I'm testing a mailbox move from Exchange 2016 database to different database that hs different mailbox quota . I can create a new migration batch for the user and it completes in short order, but the mailbox is not moved. The number of Total, Synced, Failed, and Successful mailboxes for the batch is zero. I get a notification email saying the batch completed successfully, but no mailboxes were moved or synced. When I look at the details of the migration batch in EMS I see that the ValidationWarningCount is 1 and the ValidationWarnings show, "Error:The user already exists, but the migration batch that includes it couldn't be found. Before you try migrating the user within a batch again, please remove the existing user by running the Remove-MigrationUser cmdlet." Whoever wrote that error message deserves a raise. MUCH better than the "Error code 2" I...