Since the SGC is classified, everything is routed through Peterson AFB. Carter's would be samantha.carter@peterson.af.mil

Yeah, I've given John Sheppard's address as john.sheppard@peterson.af.mil, especially as I can't imagine that john.sheppard@atlantis.af.mil would be at all good for security! Plus, his brother says in Outcast, "I contacted your unit commander at Peterson," so I have to assume John's email gets routed through there as well.