Have you been looking at running Exchange Server with replication for HA or DR?
Check out the Exchange Solution Reviewed Program paper that details a 60k user Asynchronous replication solution. The numbers in the paper are fairly impressive, especially since the config is using a real world layout!
If you don’t have the huge distances to cross, maybe the Synchronous replication solution would be helpful as well. This one also uses a real world layout that an average customers can safely implement without overspending for the sake of benchmarking…..
