Remove a Server
You can use the Remove Server option on the Action/All Tasks menu in System Manager to remove a server from Active Directory. You should regard this option as a last resort disaster-recovery tool that you can use if you cannot use the setup program or commands in Control Panel to uninstall Exchange.
To remove a server using Action/All Tasks:
Right-click the server, select All Tasks, and then click Remove Server. The following error message appears:
Are you sure that you want to remove Microsoft Exchange server servername? Performing this action may cause you to lose mailbox data, public folder data, or configuration data related to this server. If you are certain you want to remove Microsoft Exchange from a running server, instead please run Remove from the Add/Remove Programs function in the control panel.