An issue that came my way in response to System Mailboxes in Exchange 2010 & How to recover them is that the exchange admin can’t find any of the arbitration mailboxes while running Get-Mailbox –Arbitration. The command runs without any errors, but doesn’t bring the arbitration mailboxes back. The accounts are in AD and are visible.
The issue was that the environment had a root domain and multiple child domains. The arbitration accounts are in the root domain by default and the Exchange Shell session was only looking at the child domain. To fix the issue, you need to run the following command, so that the scope of the search is changed to the forest level.
Set-ADServerSettings –ViewEntireForest $true
Once the above command is run, Get-Mailbox –Arbitration gives the correct output.