In Microsoft Exchange 2010 and 2013, There are 3 Arbitration system mailbox used to store organization data such as administrator audit logs, metadata for eDiscovery searches, and Unified Messaging data.
Mailbox databases that store Arbitration mailboxes cannot be deleted before the Arbitration mailboxes are moved to another database.
To move Arbitration mailboxes use the cmdlet below:
Get-Mailbox -Arbitration | New-MoveRequest -TargetDatabase “Mailbox Database 3052606571”
