I had a functioning Exchange 2016 server. Migration between databases was all fine. I installed another Exchange 2016 to replace the old one. Install went fine, all mailboxes were moved but I had to do it from powershell because the UI was throwing up error about System Attendant mailbox being inaccessible. After the migration was done and mail flow is functioning, I want to resolve this issue to prevent future problems. After reading forums and articles online, I noticed that "Microsoft Exchange System Attendant" service is not there at all, on either server. I don't know if it was there before but I experienced no issues with the old server. But the SA service is not there on either server now. I am stumped and can't find anything online about this. I only noticed it was missing after I changed the System Attendant HomeDB attribute in ADSI Edit and wanting to restart the service to make the change effective.
SnapOverflow
As joeqwerty said, the SA service was removed in Exchange 2013 and the configuration object is still residing in configuration partition.
To troubleshoot the SA issue, you could check whether all the arbitration mailboxes are running well in the database of the old server with the command “Get-Mailbox -Arbitration | fl Name,Database”, if the arbitration mailboxes don’t locate in the database(Empty value), you could try to re-enable them:
If the above inspection isn’t problematic, you could check whether the database is mounted with the command “Get-MailboxDatabase -Identity -Status | fl Name,Mounted”, if not, you could remount it:
In addition, you could also check whether there were some events happening in the Event Viewer when you tried to use the UI to move all the mailboxes.