As Fred said, if individuals' mail user-agents do not apply
either In-Reply-To: or References: headers when the user uses a
"Reply" function, the users have to realize that they are into
"error recovery" already when MHonArc attempts to thread their
So it is not a_priori unreasonable to ask list subscribers with
mail tools that are that far off the norm to manually repair the
subject line on replies if they care about the threading in the
archive. That is the big If where some sort of consensus from
the list subscribers is critical. Asking for conformance to
standard operating procedures that require manual intervention
should be based on an overt "is this trip necessary?" check with
the list membership.
Incidentally, what do people think would be the "right" way to
list and link messages when someone states the Subject: as
"new_subject (was 'old_subject')"? You may or may not have a
Message-ID to correlate.