Did you nuke your Exchange server or "accidentally" delete it? Fortunately, Microsoft has a way to revive it! Here are the steps as mentioned in the following KB article: http://technet.microsoft.com/en-us/library/dd876880.aspx
- Reset the computer account for the lost server. For detailed steps, see Reset a Computer Account.
- Install the proper operating system and name the new server with the same name as the lost server. Recovery won't succeed if the server on which recovery is being performed doesn't have the same name as the lost server.
- Join the server to the same domain as the lost server.
- Install the necessary prerequisites and operating system components. For details, see Exchange 2010 System Requirements and Exchange 2010 Prerequisites.
- Log on to the server being recovered and open a command prompt.
- Navigate to the Exchange 2010 installation files, and run the following command:
Setup /m:RecoverServer - After Setup has completed, but before the recovered server is put into production, reconfigure any custom settings that were previously present on the server.
