So, that line is it for matching commentless message-ids. To make it into a
condition and break it up into semi-readable chunks:
:0
* ! ^Message-Id:[ ]*<[ ]*("([^"\]|\\.)*"|[-!#-'*+/-9=?A-Z^-~]+)\
([ ]*\.[ ]*("([^"\]|\\.)*"|[-!#-'*+/-9=?A-Z^-~]+))*\
[ ]*(_at_)[ ]*\
(\[[ ]*([^][\]|\\.)*[ ]*\]|\
[-!#-'*+/-9=?A-Z^-~]+([ ]*\.[ ]*[-!#-'*+/-9=?A-Z^-~]+)*)\
[ ]*>
Hmm, maybe I'll start logging ids that match that condition.
I did ;-)
It matched two messages so far. One message-id was clearly bogus,
but here's the other one (mailing list with 1 msg/week, no spam):
Message-Id:
<199803251729(_dot_)LAA10847(_at_)wuarchive(_dot_)wustl(_dot_)edu(_dot_)>
Is your regexp incomplete wrt trailing dot in the domain part, or
is the MUA/MTA broken?