There are two major contenders, as far as I can tell:
Majordomo is, I believe, the more modest of them, in case you want to
run something on other than Unix. I had an extended fight with it
before I got it to run pretty much correctly on a RISC/6000 under AIX,
so check with me if you run into that. The author of Majordomo runs
this very list so I think you get it from ftp.greatcircle.com.
Listproc, written by someone at Boston University, is so much like
LISTSERV that it was called listserv for Unix until the author of
LISTSERV for CMS (Eric Thomas?) objected that he was getting bug
reports on this stuff that was not his. The Unix version is now
called listproc (listprocessor) and may be available from bu.edu
so ask archie. I haven't ever built listproc, so I too will be very
interested in hearing any comparisons.
I now have mail scanning programs using awk, and again usin Perl.
It only took me a few hours when I finally had to do it today, but
it pleases me to have an awk meta-scanner (builds particular scanners
from very simple tables of values and patterns) in just a couple of
pages of fairly simple code. I even built a debugging version which
tells you more than you wanted to know about how it's working.
I can't yet use the Perl version on my NeXT due to some assembler
error during make. If you have a clue how to deal with that, it's
the only request I make in this missive.
ps None of this is authenticated, but the author would appreciate
(but as just above, will not request) hearing about any errors.