Frank Ellermann <nobody(_at_)xyzzy(_dot_)claranet(_dot_)de> writes:
Hm, that's partially a misunderstandig. My example is very
simple: The MSA forces me to use the correct MAIL FROM, a
MAIL FROM matching my account.
That's good and as it should be. Unfortunately it does not
add a matching Sender (allowed by 2476 8.1 "MAY"), so what
you (as recipient) get from me is a correct MAIL FROM with a
_different_ 2822-From (= nobody(_at_)xyzzy).
In these circumstances, would it not be possible for the MUA to add
the Sender: header before passing the mail to the MSA? Or is the
problem that you do not know which MSA will be used (and hence what
the Sender: header should contain) at the time you compose the mail?