as far as i know, the mailserver on panther is not sendmail any more by default.
apple has decided to switch to postfix, which is a little easier to configure.
postfix does not loose rejected mails as sendmail does (sendmail panic)
but as far as i am concerned:
i will try to put sendmail on panther as soon as i will put it on my G4.
itīs also possible to have sendmail and panther installed on the same system.
just need some changes in the /etc/hotconfig and in the /System/Library/StartupItems/
an if you realy want to do this, it would be even possible to have them running at the same time using diffrent ports
greetings from germany