Can not remove Exchange 2010 because there are arbitration mailboxes
When you try to remove the first DB in Exchange 2010, there are a few arbitration mailboxes that will prevent database deletion. You have the choice of moving, removing, or mail-disable these mailboxes. Since you cannot see these in the Exchange Management Console, you need to launch Exchange Management Shell (EMS).
To list the arbitration mailboxes, run the following cmd:
To narrow it down to a specific database, you can edit this to:
Get-Mailbox -Arbitration -Database <DB name>
Once you have your “get” command returning the correct list of mailboxes, it’s time to move, disable or remove them. Disabling the last arbitration mailbox is not allowed, so it is recommended to move them as the first preference here.
Get-Mailbox -Arbitration -Database <db1> | New-MoveRequest -TargetDatabase <db2>
Get-Mailbox -Arbitration -Database <db1> | Disable-Mailbox -Arbitration
Get-Mailbox -Arbitration -Database <db1> | Remove-Mailbox -Arbitration -RemoveLastArbitrationMailboxAllowed