When you want to recover an Exchange 2007 or Exchange 2010 server you can use the /RecoverServer switch in setup.com. To accomplish this, you have to reset the computer account in Active Directory. After resetting the account you can join the newly installed Windows Server (with the same name of course) to the Active Directory.
When you want to reset the computer account, you open Active Directory and Computers and right-click the computer account. When you select "Reset account" you will see "Resets the password for the current selection.".
Initially this might look strange, but it is not. A domain joined client uses a secure communications channel between the client and the domain controller. This is also known as the 'security channel'. This password is stored with the computer account in Active Directory. When resetting the computer account, you are actually resetting the password mechanism and the new computer will setup a new password synchronisation with Active Directory.
For more information see the Microsoft knowledge base article KB216393: