publisher says something like:
"mydomain.example.com: only nnn.nnn.nnn.nnn applies_to 'MAIL FROM'
# we know this means our mail might not be forwarded # but
we're OK with that.
Sorry, Jon, that won't work.
Suppose alice(_at_)mydomain(_dot_)example(_dot_)com sends mail to
bob(_at_)alumni(_dot_)almamater(_dot_)edu(_dot_) But bob has set up
bob(_at_)alumni(_dot_)almamater(_dot_)edu to bob(_at_)company(_dot_)com
Harry, it breaks forwarding. We know. In the example I gave you at your
request: The publisher knows; a legitimate sender must know; the recipients
Please do me the courtesy of reading what I've written (and accept my
apologies if I didn't make it clear). I don't believe it's a terribly
obscure point that I'm trying to make.
Now company.com does the check of MAIL FROM and erroneously rejects the
mail because it is coming from alumni.almamater.edu's MTA which has the
wrong IP address.
This is not erroneous. It's in accord with the published record and with
the final recipient system policy. It's correct.