I came across the error below while decommissioning Exchange 2010 servers in 2003-2010 co-existence environment (test lab). I was trying to remove the arbitration mailbox using Get-Mailbox –Arbitration | Remove-Mailbox –Arbitration –RemoveLastArbitrationMailboxAllowed and got the error below.
The Arbitration Mailbox “mailbox name” is used by Exchange and can’t be removed.
I can see the arbitration mailboxes using Get-Mailbox –Arbitration. I was able to remove one of the system mailboxes using the command above (The screenshot above only has one system mailbox, the other one being removed).
If you are in a multi domain environment, especially with a blank root domain, you need to run Set-ADServerSettings –ViewEntireForest $true before you can list the arbitration mailboxes using Get-Mailbox –Arbitration.
Though I can use ADSIEdit and remove the AD account, I was thinking of removing the Exchange attributes the proper way, using the Shell. I tried disabling the arbitration mailboxes and it worked (surprise). The command I ran was Get-Mailbox –Arbitration | Disable-Mailbox –Arbitration –DisableLastArbitrationMailboxAllowed
I couldn’t remove the mailbox, but I could disable it. Go figure