[Mailman-Users] spam gatewayed from Usenet to mail bypasses our spam filters

[skip at pobox.com]

With the help of the python.org postmasters I figured something out about
spam on the python-list at python.org mailing list over the weekend.  I was
confused that some seemingly obvious spams made it through to the mailing
list subscribers.  Then I noticed that it didn't appear these spams had even
seen the spam filter.  The headers the filter adds were missing and I could
never find their Message-Id's in the spam filter's logs.

Mailman operates the bidirectional gateway between the Usenet newsgroup
comp.lang.python and the python-list at python.org mailing list.  When it sees
a Usenet message on the one side it distributes the posting directly to its
subscribers, and vice versa.  Because Usenet postings don't arrive by email
the spam filtering we have in place (which occurs before Mailman sees a mail
message) is not done.  Mailman happily passes such unfiltered mail on to the
list.

I still haven't figured out quite how to solve the problem.  In theory we
could use some other tool to perform the gateway operation.  Instead of
passing Usenet postings directly to Mailman it would mail them to
python-list at python.org where they would get the spam filter treatment before
Mailman sees them.  I'm still thinking about the full ramifications of that.
It might be easier to get Mailman's news-to-mail gateway to mail incoming
Usenet messages to the list address instead of directly distributing them to
the subscribers though.  I don't believe Mailman does that out of the box
(but I would love to be wrong here).  Has anyone tried implementing that?
If so, got a patch or a recipe for how to configure Mailman to operate this
way?

Thanks,

-- 
Skip Montanaro - skip at pobox.com - http://smontanaro.dyndns.org/