my network :-
Domain controller - os windows 2008 std R2
Exchange - os windows 2008 std R2/ exchange 2010.
newly installed network.
oulook was connecting and owa also ...
from yesterday , the outlook stopped connecting to exchange and owa is working perfect still.
error is " cannot open your default email folders. microsoft exchange is not available .Either there are network problems or the exchange computer is down for maintanance.