Original Source: http://www.mikepfeiffer.net/2010/04/how-to-recreate-the-system-mailboxes-in-exchange-2010/
When you install Exchange 2010, several system mailboxes are created in the root of the Active Directory forest. The actual Active Directory accounts for these mailboxes are disabled and not intended to be used by administrators, and instead are used for things like the moderated transport system, etc.
The system mailbox descriptions and names are as follows:
- Discovery– SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}
- Message Approval – SystemMailbox{1f05a927-xxxx-xxxx-xxxx-xxxxxxxxxxxx} (where x is a random number)
- Federated E-mail – FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042
So, what happens when someone deletes these mailboxes and they are purged from Exchange? Well, the solution is simple. You just need to use the Enable-Mailbox cmdlet with the -Arbitration parameter, for example:
Enable-Mailbox "SystemMailbox{1f05a927-409a-4693-9ea1-c71cc379dab7}" –Arbitration
Run the above command for each mailbox as needed.
What if the Active Directory Accounts are Deleted?
If the system mailbox accounts are deleted from Active Directory, you can restore them by re-running the PrepareAD process using Setup.com from the Exchange media:
Setup.com /PrepareAD
After the Active Directory accounts have been recreated, you can create mailboxes as shown in the first example using the Enable-Mailbox cmdlet. Hope this helps!
[Update] MSDN Article http://technet.microsoft.com/en-us/library/gg588318.aspx