What's the fundamental distinction between an agent redistributing mail
to a list and another agent forwarding mail to, say, a new email address
given in a .forward file? Is it only that the list redistribution
rewrites the Return-Path: whereas .forward processing doesn't? Is this
why you see list redistribution as more of a MUA function than an MTA
one?
I don't know whether it is a fundamental distinction, we just recognize
that there's a place for each. Offhand, I would suggest that
- forwarding is appropriate for a very small # of addresses,
list handling is more appropriate for a larger number
(so that for instance the sender of a message to a list doesn't
get a bounce message for every list member whose mail delivery fails)
- forwarding is appropriate when the relevant addresses are all
under control of the same person (or of a small # of people)
(so that changing the destination of error reports is not
so much of an issue)
- forwarding is more appropriate for private redistribution than
for public lists to which anyone may subscribe.
as for the MUA/MTA distinction - many public lists do things like
munging headers, interpreting message content, and/or filtering
message content, all of which are arguably UA functions.
Keith