ensu: Karl Malden, right?
Wayne: Not open-relay I hope? That could explain the problems because operating as an open-relay would make the server you're on blacklisted and some (eventually all) mail servers would refuse to have anything to do with it.
To people in general:
Knowing nothing about mailservers and starting one is the equivalent to a passenger getting into a jumbojet and start taxing out... Atleast buy a book on the subject. The consequences can be serius, not only for you but, but also for the server you're on.
