Charles Lindsey wrote:
If the author has some special
requirements of his own, he will include his own MFT (whatever) header,
and the list owner will do nothing further. We were discussing the case
where the author (through ignorance or laziness) did nothing and left it
to the list owner to supply a sensible default, consistent with the
culture of the list.
Others have addressed some of your assumptions. In addition, you
seem to be assuming that either
a) a human list manager will manually deal with every such message,
which is impractical
or
b) that some software will insert some canned field; given the wide
variation in possible author intent, that is likely to be wrong
much of the time.
Moreover, you seem to be assuming that the only case of interest is
formally managed lists. That ignores cases where correspondence
takes place among a group of people with no list expansion at all.