Running Unity 4.05 with Failover, Exchange 2000 offbox, Voice Mail only config. My Exchange boxes are DL380 G4's with dual cpu with a lot of disk space left. Wondering how many exchange mailboxes these servers will support before I need to add new Exchange servers. I currently have about 2000 users on each server and my exchange data base runs about 8 - 9 gb on each server. These servers also act as the DC/GC's for the Unity standalone AD domain. I am having no issues but need to plan for the future. I expect to be upgrading to Unity 7 next year.