🚀 go-pugleaf

    Date: Mon, 17 Nov 86 19:48:06 -0800
    From: Marshall Rose <mrose at nrtc-gremlin.arpa>

    there is a difference between working correctly and working.  Working
    correctly is to ignore sender and return-path.  However this is not
    often working...there is neither perfection nor diligence in the
    Internet.  It is better to know that you can fall back on sender
    and/or return path in case you have to (when working on a poorly
    constructed message), than to just say "you can't reply to that".

There's a difference between DWIM and incorrectness.  Your mail handler
may reasonably complain "I can't reply to that" and ask the human for
help; it can't reasonably figure out which of From, Sender or Return-Path
might interest the user (for instance, if I want to send a message to
someone who will fix it up I might send a message to the Return-Path,
whereas in a legitimate reply I might be able to construct a valid
destination address).

For purposes of replying there isn't much difference between Return-Path,
Sender, and Subject.  They all have inappropriate semantics.  The machine
shouldn't fake out naive users by using random information.