On 2025-09-08 at 14:37:59 UTC-0400 (Mon, 8 Sep 2025 18:37:59 +0000)
John, Chris via Postfix-users <chris.j...@bms.com>
is rumored to have said:
I have a postfix 3.5.2 system that accepts messages from internal
hosts and relays to internal destinations and to an email perimeter
that delivers to external (Internet) domains.
Are the internal hosts runniong Popstfix or something else? Sendmail,
for example?
The issue I'm seeing is regarding external domains that do not follow
DNS best practices and have CNAME records published for the same
domain that their MX records are published for.
What I end up with is the recipient being changed from the intended
domain to the value of the published CNAME.
That is a default behavior of Sendmail in many distributions and
historically. It is consistent with the historical formal meaning of the
CNAME record, which is that the result of the CNAME query is the
*PROPER* name which should be used instead of the alias name.
As Wietse has already noted, the log lines you provided state clearly
that the message arrived and was delivered with the same recipient.
Also, this log line provides a clue:
[...]
Sep 2 01:35:39 mailhost postfix/cleanup[26989]: 4cGDwq3YqbzjB8nV:
warning: header Received: (from otosadm@localhost)??by use1otomprd01
(8.15.2/8.14.7/Submit) id 5825ZbvF012075??for katherine...@bizpro.cn;
Tue, 2 Sep 2025 01:35:37 -0400 from unknown[x.x.x.x];
from=<mg-procurement-operat...@example.com>
to=<katherine...@web.b51.vhostgo.com> proto=ESMTP helo=<use1otomprd01>
That's a Sendmail-constructed Received header, being logged due to a
Postfix header_checks match. It shows the initial submission of the
message using the alias domain name. Sendmail rewrites that address to
use the canonical name.
This can be fixed on the machine running Sendmail by changing flags for
one of the mailer definitions. See the Bat Book or Sendmail ops guide
for details.
--
Bill Cole
b...@scconsult.com or billc...@apache.org
(AKA @grumpybozo@toad.social and many *@billmail.scconsult.com
addresses)
Not Currently Available For Hire
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