As I'd mentioned before, Aqua uses the EWS network protocol to connect to Exchange servers.
It does not support ActiveSync, the other Exchange network protocol, because of licensing complications.
Most corporate servers support both EWS and ActiveSync. Mail Droid (which is pretty popular) uses EWS.
However... Hotmail does not. It only supports ActiveSync.
"Standard" mail apps that come preinstalled, and some third party ones, are from companies that have ActiveSync licenses.
It's much easier when you're a company like Sony / Samsung / HTC / LG / ASUS than it is for me.