Simon Josefsson writes:
The neat thing with NoReply is that recipients aren't required to be
aware of the specification
It's certainly a good idea to avoid unnecessary upgrades.
In this case, however, the behavior of ancient MUAs (namely, always
including the reply recipient list as part of the followup recipient
list) is fundamentally incompatible with what mail users want.
This is why I rejected pure sending-side solutions when I was designing
Mail-Followup-To several years ago. This is also why quite a few MUAs
have, in fact, been upgraded to do a better job---in particular, to
support Mail-Followup-To.
---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago