Most 'test message' users on my lists are not Replying to a posting to
begin with, but creating a new message from scratch, either because they're
just curious 'does this work' or they've been dropped the previous week
from DNS/quota bounces and very sensibly infer that everyone else on the
list must have stopped posting for some reason. :) Either way, Reply-to
munging is a non issue in this respect. No matter how piously we observe
the absolute letter of an arbitrary and somewhat misapplied RFC, we are
still going to get test messages.
If you want to minimize spam on your lists, allow only members to post, and
disable the membership listing commands. I used to use bushels of filters,
now I don't need any of them. If you don't want to force people to join
before they can look up good info from your list postings, make searchable
archives available on the web. If they want to post, they can join.
If you want to know what people in your topic specialty would really like
in a mailing list, don't just survey the people who like what you're
already doing well enough to be current members. This invariably makes you
look like a genius because everyone who hated your list has already left
and isn't surveyed. Instead post a Web based survey and advertise it in
other forums and publications for your specialty (model rockets, Janis
Joplin or whatever). By giving those people what they want (consistent
with your own aims and principles) you can grow your email community rather
than just patting yourself on the back.