but Reply-To should probably be deprecated in favor of something that
specifies the *complete* recipient list rather than just a replacement
for From.
A large part of the problem is that some people think that
(a) Reply-To specifies the complete list of recipients that the author
thinks should receive replies
while other people think that
(b) Reply-To specifies a list of recipients to be used instead of the
From address when directing replies.
I'd argue that the proper function is (a) but the reality is (b).
(I seem to recall that Dave Crocker once argued that the intent was
(b), but I may recall incorrectly.)
Meaning (b) of the Reply-To field is so deeply entrenched that I
think it would be impossible to get the world to use Reply-To with
meaning (a). So we seem to need a new field to have meaning (a).
Mail-Followup-To seems to fit the bill.
One of my concerns with MFT is that it's being promoted and used as a
way to suppress some kinds of duplicate copies of replies. There's a
conflict between using a field like this to suppress duplicate copies
and using the same field to indicate whether the author thinks replies
should go to somewhere besides "everyone who received this message":
- The recipient's user interface needs to act differently in these two
cases - in the first case it's just a normal "reply all" since
everybody is getting a copy of the message. In the second case the
replier needs to be aware that the reply is going to a different set of
recipients than is normal, and it seems appropriate for the MUA to
provide some kind of alert to that effect.
- If the replier only wishes to reply to some of the recipients, and
doesn't know which recipient addresses are contained in other recipient
addresses (via lists or aliasing or whatever), the use of MFT to
suppress duplicates fails. It can be argued that this is a marginal
case and not worth fixing. However, enough people react strongly to
receipt of any duplicate copies of a reply that it might still be an
important case even if it happens rarely.
-Keith