But if we really want to have recipients' MUAs suppress duplicates
when
composing replies, we should do it differently than with the
Wide-Reply-To or Mail-Followup-To field. For instance, we could have
a
field of the form
Suppress-Duplicate: address1, [address2, address3, ... ]
which says that if a reply is being sent to _any_ of address1,
address1,
etc., don't send a separate copy to the From address.
That has the same lack of traction that affects Wide-Reply-To and
Mail-Followup-To -- every UA has to be modified for it to work.
Though MTAs shouldn't munge address fields, it also requires MTAs
that do so to be aware of the field and its syntax and semantics
and to modify it in a manner consistent with any modifications to
other address fields (and envelope addresses).
You are of course correct. I think this is better than
Mail-Followup-To for suppressing duplicates, but I didn't say it was
without problems.
The nice thing about suppressing duplicates at recipients' MUAs or
message stores (rather than at the MUAs where replies are generated) is
that the benefit is immediately by those whose MUAs or message stores
are upgraded to support this. But as we've seen, that approach also
has problems.
Keith