I was at a huge client, that has a complete mess on it's 2000 AD, there are several domain controllers, and for some reason almost every single one of them assumes it is the master server for several roles.
As you can imagine, their network is not functioning properly and exchange 2000 just stoped sending and receiving msgs. From the queue on the server, you can see that messages are pending AD resolution.
I plan to choose a "healthier" looking domain controller, demote/remove all other DCs, so that I can have a single server with all the roles, and then promote a new DC for fault tolerance. I don't know if this will solve the exchange problem, but it seems to be a necessary step towards resolution of all problems.
What do you think?