Spam and other unwanted electronic-mail may be controlled by a system in which a given external message transfer agent using a given Internet protocol address and a given domain name is limited in the number of connections that it may make and the number of messages it may deliver over a given time period. Based on the performance of that external message transfer agent, the passage of time and the number of connections, its assigned connection limit may be increased so that progressively trust is increased and more message connections and a higher number of messages delivered may be permitted.