You need to ensure that Server1 can replicate mailbox databases from DAG1.

You have an Exchange organization. All servers in the organization have Exchange Server 2010 SP1 installed.

The organization contains a database availability group (DAG) named DAG1. DAG1 contains three Mailbox servers including a server named Server1.

Server1 fails. You restore Server1.

You need to ensure that Server1 can replicate mailbox databases from DAG1.

What should you do first?

A.
Remove the Default Mailbox database from Server1.

B.
Modify the GUID for Server1.

C.
Remove the object for Server1 from DAG1.

D.
Disable log truncation for the mailbox databases in DAG1.

Explanation:
Remove-DatabaseAvailabilityGroupServer -Identity DAG1 -MailboxServer MBX1 -ConfigurationOnly

High level steps to recover Server1:

1) Remove the failed server’s configuration from the DAG by using the Remove-DatabaseAvailabilityGroupServer cmdlet. Because the DAG member being removed was offline and could not be brought online, you must add the ConfigurationOnly parameter to the above command.

2) Reset the server’s computer account in Active Directory.

3) Open a Command Prompt window. Using the original Setup media, run the following command: Setup /m:RecoverServer

4) When the Setup recovery process is complete, add the recovered server to the DAG by using the Add-DatabaseAvailabilityGroupServer cmdlet.

5) After the server has been added back to the DAG, you can reconfigure mailbox database copies by using the Add-MailboxDatabaseCopy cmdlet.

Reference:

http://technet.microsoft.com/en-us/library/dd638206.aspx