Some of the other people to work on sendmail and their contributions include:
Lennart Lovstrand - dbm support & the separate rewriting of headers and envelopes
Neil Rickert and Paul Pomes - fixes and enhancements to m4 configuration, other code enhancements and bug fixes
Paul Vixie - miscellaneous code improvements
Claus Assman - miscellaneous code improvements and a pile of anti-UCE enhancements
The effect of all of this was that the product itself had evolved significantly but it was so diverse that many companies had written their own special versions and maintenance was becoming an unmanageable process. Versions became so dissimiliar that administrators had to learn a new version everytime they switched oeprating system. The same situation exists today, but thankfully, with the release of version 8 many of the improvements and enhancements included in some of the code forks were included in the main body of code and the reasons for using any of the other versions were rapidly decreasing. In today's environment there is little reason to use a forked version as the main code branch includes just about everything that's available, or needed.
The version of sendmail (8.9.3) included with Red Hat Linux 6.1 and 6.2 is derived directly from the source code available from http://www.sendmail.org. It contains several enhancements which Red Hat, Inc. has provided to make it easier for you to use and to increase security.