> > Michael Fox skrev den 2017-09-21 19:52:
> > > I have a problem that seems to have started when I upgraded from
> > > 14.04/Postfix 2.11.0 to Ubuntu 16.04/Postfix 3.1.0. It involves the
> > > From:
> > > and Return Path: addresses seen by recipients of mail sent from a
> > > virtual
> > > domain on that machine.
This problem turned out to be a DNS issue. The Postfix 3.1.0 machine's
virtual domain in the From: address was entered in DNS with a CNAME record
pointing to the gateway machine (because they are, indeed, the same
address). When it was changed to an A record, the problem went away.
Evidently, the user that was certain that the problem only started after the
upgrade was, uhm, mistaken. The problem also didn't occur on a separate
Postfix 2.11 machine because it's DNS entry was correct.
BTW, the mail provider found that the default sendmail config and their own
customized config both rewrote the From: header when the From: address was
for a domain that had a CNAME record. They said this is a config option in
sendmail and they prefer to operate this way. Interesting that my other
Postfix machines don't do this, nor do many other large email providers.