The mailing list for listmasters using Sympa

[address@concealed (Kendall Libby)]

We're having a problem with a badly behaved list server sending junk
to our sympa (5.3.4) server, and I think that sympa isn't handling it
as well as it should.

Initially, their server tries to send a message to a moderated list
and sympa replies with the usual "you've been moderated, etc" reply.
But that leads to them replying to sympa with not only an 'unknown
command' message, but also a second 'help' message.  This then causes
sympa to reply to both; lather, rinse, repeat.

Now I can - and have temporarily - added their 'list' address to the
loop_prevention_regex but it I would have thought that sympa would
check for a null Return-Path: header before replying.  Instead, it's
only looking at the From: address.  

Admittedly, I haven't been able to wrap my brain around all of the
relevant RFCs, but it seems like this is an oversight on sympa's
part.  

Any thoughts?

K.