[Mailman-Users] stopping cross posting?

[Stephen J. Turnbull]

Mark Sapiro writes:
 > On 10/10/2016 05:44 PM, Adam Morris wrote:

 > > People send messages to a list I run as well as other lists that I have
 > > nothing to do with.
 > > 
 > > When people reply to the message sent to other lists the replies go to
 > > my list as well as the list they replied to.
 > 
 > If the person replying does a reply-all and doesn't remove the lists of
 > which she is not a member from the recipients.
 > 
 > > Is there a way to stop this apart from asking people to only send the
 > > message to one list at a time?

Aside from Mark's suggestion:

 > Attempting to train your list members is futile[1]. What you can do is
 > set Privacy options... -> Recipient filters -> max_num_recipients
 > to 2.

I agree about training members.  It's not worth the grief.  Most MUAs
have poor user interfaces, but once people get used to them, they can
be really efficient about the things they do 20 times per session.
Asking them to change *anything* in their habits is quite painful for
them, because it really slows things down and they feel bad about
forgetting (or "forgetting") to do the right thing, which they do
frequently.  Some get really upset about moderation delays and
"discrimination".

(1) If there are lists which are consistent offenders, you can put
    them in Privacy options... -> Spam -> Header filter rules, with

    ^(to|cc):.*\botherlist at example.com

(2) If you aren't restricting posting to members, use 
    Privacy options... -> Sender filters -> Generic nonmember action
    to prevent members of otherlist who aren't members of your list
    from posting.

(I see you're already doing the latter from a later post.)

 > Also this creates another problem.

The "filter out otherlist using filter rules" solution doesn't cause a
problem for users who reply-all because there are several addressees
who aren't on the list or whatever.  Of course it does require you to
know the lists that frequently cause issues, and it also causes delays
for "legitimate" cross-posts, if your list policy recognizes any.

The "restrict to members" solution isn't appropriate if there are more
than a few nonmembers, or there are unknown nonmembers, who should be
allowed to post.  (It's possible to have exceptions for some
nonmembers, but this gets annoying fast if there a more than a
handful, or you don't know who they are until they get held and
complain or worse go away.)

Steve