The Exchange protocol is orders of magnitude richer than IMAP, but it's not standard (which is why it's totally proprietary :)).
But is it fair to say that the Exchange protocol is a protocol in the same sense as IMAP, or even a true protocol at all?
Not in the same sense. Making two programs from the same organization talk to each other is easy peasy compared with making many and different programs from many independent and competing organizations interoperate. Both technically and politically.
Whether it's a protocol at all... I guess that hinges on the definition of protocol. Doesn't really matter, does it?
--Arnt
