He went on to create several well-known network and security tools, including the Security Administrator's Tool for Analyzing Networks (SATAN) and The Coroner's Toolkit with Dan Farmer. He is also the creator of the popular MTA Postfix and TCP Wrapper.
If you're designing a major mail system then you're also going to be asking yourself the question should I use more than one kind of MTA, and if so which should go where? Hopefully this article can help.