Back when Exchange 2000 came out, Microsoft recommended installing Exchange on the domain controller, and we did. But later, Microsoft recommended installing it on a member server. I have Exchange 2000 server running on a Win2000 server domain controller (DC), and it is the first server in the AD forest. I have two other domain controllers in the forest. How do I demote the Exchange server to a member server and make one of the other domain controllers the master domain controller? Will this affect the mail coming into the Exchange server?
I don't recall Microsoft ever recommending that you install Exchange 2000 on a domain controller. In fact, my understanding is that the company's recommendation has always been the opposite: You should always put Exchange 2000 on a member server.
You really should not encounter any issues when you DCPROMO the Exchange/Domain Controller system down to a member server, as long you do not make this new DC hold any FSMO roles and as long as it is not the only GC (global catalog). If it does hold FSMO roles, then you'll need to transfer them to another DC. See Microsoft Knowledge Base article 255690, How to View and Transfer FSMO Roles in the GUI.