To remove the Exchange 2007 server object in Active Directory
Install ADSI Edit.
Launch ADSI Edit. To do this, click Start, click Run, type adsiedit.msc in the text box, and then click OK.
Locate the Exchange server object by going to the following location: CN=Configuration, DC= Domain Name, DC=com, CN=Services, CN=Microsoft Exchange, CN=<Organization Name>, CN=Administrative Groups, CN= <Exchange Administrative Group>, CN=Servers, CN=<Server Name>.
Delete the server object.
Remove the Exchange server’s machine account from Security groups Exchange Servers and Exchange Install Domain Servers.