Bruce Lilly writes:
Something like MFT, for instance, requires changes to senders' and
recipients' UAs
One of the basic goals here is for followups to exclude the sender's
address upon request from the sender.
The sender wants his MUA to make this request _automatically_ for any
message that he sends to various mailing lists. Old message injectors
don't have this feature, so they have to be changed.
This has nothing to do with the choice of protocol. Every protocol needs
this MUA support. Criticizing Mail-Followup-To on this basis is silly.
As for the recipient's MUA: Yes, Mail-Followup-To needs some changes,
but every one of your proposals requires vastly more changes. Again,
criticizing Mail-Followup-To on this basis is silly.
and to any MSAs and MTAs that rewrite address fields.
At this point you're inventing problems that don't exist. The software
that creates Mail-Followup-To is responsible for using fully-qualified
domain names. Subsequent transports aren't expected to, and shouldn't,
rewrite Mail-Followup-To.
The post office is expected to touch the envelope (Return-Path,
Received, Delivered-To, etc.) but should never touch the contents. It
amazes me that such a basic principle needs to be stated here.
---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago