I have been installing qmail servers for a while.
I started by using Buruce Guenter's untroubled qmail+patches RPM set, which was good, but he seems to have abandoned them.
In the last year or so, I have kept working on them, and now they are somewhat more heavily patched.
I have added:
quota (bounce over-quota immediately)
realrcptto (bounce immediately unexistant addresses)
tarpitting (add delays over n recipients)
errno patch (to make it build on RH 9 or later)
smtp auth+tls (well, smtp auth and TLS ;-)
And miscelaneous changes to the default config so that, for example smtpsuth simply works by default.
I think this is probably the easiest way to install a traditional multi-UID qmail on Red Hat-like systems.
It has been a little (not too much) work, because when you pile patch over patch over patch, usually the third one doesn't apply, and this patchset has 22 patches in it.
But... the qmail source is pretty clean for C!
I think I am going to put it on sf.net or somesuch.