Will Unity (3.1.5 or above) see all the message stores in a forest, and if so, could I connect to more than five stores if I had to (knowing it is not supported). Can you help me understand why there is a five store limit? Thanks.
OK... according folks responsible for the info in that doc (the performance team guys) this is actually not correct - they were supposed to be talking about the limit of storage groups per Exchange server, not mailstores Unity can talk to - I think that section is wrong on a few levels (it should be 4 storage groups not 5 mailstores and it doesn't have anything to do with Unity). They'll work on updating that.
Unity can handle subscriber's homed on any number of Exchange servers/mailstores that are configured to Microsoft's spec - so long as the total number of subscribers falls within the specs for the hardware/config of the Unity box you should be fine.