There was no set of gyrations I could go through to get the 6.1 update to *NOT* install sendmail. It overwrote my (rpm-installed) installation of postfix, too, without barfing on the conflicts.
I agree; this is a relatively serious problem. Sendmail should not be in the base. As a workaround, you should be able to modify the comps file yourself -- look at i386/base/comps. You could even replace sendmail with postfix there. (If you remove the sendmail rpm and replace it with postfix, make sure to run genhdlist util.) Of course, if you don't have spare HD space and/or the ability to do a network install from your own mirror, this doesn't help much.
*** Bug 10384 has been marked as a duplicate of this bug. ***
Moving to RESOVLED - DEFERRED from CLOSED - DEFERRED
Reassigning to distribution component.
Implemented in Red Hat Linux 7.3 as: redhat-switchmail-0.5.1-1.noarch.rpm redhat-switchmail-gnome-0.5.1-1.noarch.rpm