Exchange 2010: What is an arbitration mailbox?
If you are like me, you probably never heard of arbitration mailboxes until you were trying to uninstall your Exchange Server, it happens. In my case I am moving from an old Exchange server into a new one and although I moved all my user mailboxes there are this hidden arbitration mailboxes you need to move as well.
Arbitration mailboxes are used for managing approval workflow. For example, an arbitration mailbox is used for handling moderated recipients and distribution group membership approval.
This is part of the Moderated Transport features that are new in Exchange 2010.
Using the moderated transport feature in Microsoft Exchange Server 2010, you can require all e-mail messages sent to specific recipients be approved by moderators. You can configure any type of recipient as a moderated recipient, and Exchange 2010 Hub Transport servers will ensure that all messages sent to those recipients go through an approval process.
In any type of organization, you may need to restrict access to specific recipients. The most common scenario is the need to control messages sent to large distribution groups. Depending on your organization’s requirements, you may also need to control the messages sent to executive mailboxes or partner contacts. You can use moderated recipients to accomplish these tasks.
This information was obtained from Technet’s Understanding Moderated Transport if you are interested in learning more.
In short, arbitration mailboxes are where messages awaiting moderation are stored, as well as information about moderator decisions are kept. Although this might not be a feature you have implemented in your organization, most likely deleting them will cause you pain so make sure you move them to your new database as explained here: How to: Move Arbitration Mailboxes in Exchange 2010