I have Exchange 2007 SP1 enterprise. All server roles in one server. and installed Microsoft forefront security for Exchange SP1. My problem happens when i try to send a large mail ( > 1 Mb) in about 90% of transfer I get the error "connection to the server was interrupted" and sending fails. I don't know where the problem is! if i tried the same scenario with OWA, I have no problem. Any suggestions?