Demote a Domain Controller running Exchange
If you are facing the task of demoting your domain controller running exchange, because you either have a new dc added to your network and want to move some roles over to that brand new sparkling server. Then you cannot do a dcpromo /demote on the exchange server! This will cause havoc. What you must do is: Add another Exchange server to your network move the mailboxes over and deinstall exchange on the DC. Then do a dcpromo /demote reinstall exchange move mailboxes over again. This is the way with the shortest downtime