Connect to the domain controler
Launch the run dialog (Windows Key + R)
Type in the command “adsiedit.msc” et then press “OK”
Right click on the console then “Connect to:”
In the connexion dialog select “Well known Naming Context”
In the drop down menu select “Configuration”
Explode “CN=Configuration [domain]\CN=Services\CN=Microsoft Exchange\CN=[organization]\CN=Administrative Groups\CN=Servers”
Right click on the dead server and pick “Delete”
We also need to delete Database information as well, navigate to “CN=Configuration [domain]\CN=Services\CN=Microsoft Exchange\CN=[organization]\CN=Administrative Groups\CN=Databases”
Explode each items to find wich one is related to the old server, then delete it as well.