and you really want return-path / MAIL FROM to point to the place where
the sender will get the nondelivery reports resulting from mail that he
sends. (list mail excepted)
This, I think, is inappropriate. If you want a header for indicating
where non-delivery reports should go, add one;
uh, there's been a standard header for that purpose for over 20 years.
it's called return-path. and the DSN standards require that reports go there.
There needs to be _some_
way to determine the real sender of a message, at least to domain level if
not farther,
it is probably a mistake to assume that the "real sender" has anything
to do with either the From or Return-Path address, or perhaps, that the sender
can be identified with *any* email address. (in fact this is what the Sender
header was intended for, though it's been so widely misused that too late to
save it, and there's a reason that Sender isn't required to have the syntax of
an email address). but email addresses are not distinguished names. they can
be shared, and Senders can have as many email addresses as they want.
and no, it's not necessary to determine the real sender's identity, and this
might not even be desirable. an alternative proposal is forthcoming.
Keith