The first change we made in the evolution of our mail system was to add a separate machine to be ourexternal mail gateway, putting it in front of our central mailmachine for outside email. We did this for two reasons: first, wewanted to introduce some sort of system-wide anti-spam features , and second, the central mail machine washeavily overloaded by directly handling external email (partly becauseit had a very old MTA that had an unfortunately heavyweight way ofhandling incoming connections and partly because it