Sendmail without the Superuser
As an exercise in the application of the concept of least privilege, we have modified the pieces of an ordinary UNIX* mail system, sendmail in particular, to require little or no privilege in their operation.
http://www.usenix.org/publications/library/proceedings/sec4/carson.html

Setting up sendmail on a firewall, Part 1
This article discusses the implementation of sendmail on the firewall and focuses on features new to sendmail 8.9.3.
http://www.wkeys.com/articles/swol/Apr_99.html

Setting up sendmail on a firewall, Part 2
This article covers the intricacies of sendmail configuration file and shows you how to generate, build, and test a config file for your firewall.
http://www.wkeys.com/articles/swol/May_99.html

Setting up sendmail on a firewall, Part 3
This final article in the series covers installation, optional features, and testing techniques. An example of configurations for a special situation is described.
http://www.wkeys.com/articles/swol/Jun_99.html