In the Exchange Powershell-based Console Management :
Get-Mailbox -Database "[Database ID]" -Arbitration | Remove-Mailbox -Arbitration -RemoveLastArbitrationMailboxAllowed
Random tech stuff
In the Exchange Powershell-based Console Management :
Get-Mailbox -Database "[Database ID]" -Arbitration | Remove-Mailbox -Arbitration -RemoveLastArbitrationMailboxAllowed