I have a standalone ZCS host at schnell.mydomain.com. It is the primary MX and is configured as such in the domain records. If I receive an unknown user to mydomain.com, zcs postfix appears to do an A-name lookup for mail.mydomain.com:
Jun 13 15:38:32 schnell amavis: (24120-20) FWD via SMTP: <email@example.com> -> <firstname.lastname@example.org>,BODY=7BIT 250 2.6.0 Ok, id=24120-20, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 825D6624261
Jun 13 15:38:32 schnell slapd: conn=25828 op=24 SRCH base="" scope=2 deref=0 filter="(&(|(zimbraMailDeliveryAddress=bloobi@mydo main.com)(zimbraDomainNameemail@example.com))(z imbraMailStatus=enabled))"
Jun 13 15:38:32 schnell amavis: (24120-20) Passed CLEAN, [22.214.171.124] [126.96.36.199] <firstname.lastname@example.org> -> <email@example.com>, Message-ID: <1213385874.9671.162.camel@blah>, mail_id: J15VSofLmU6O, Hits: -1.998, size: 1916, queued_as: 825D6624261, 447 ms
Jun 13 15:38:32 schnell postfix/smtp: 12DF5624229: to=<firstname.lastname@example.org>, relay=127.0.0.1[127.0.0.1]:10024, delay=0.48, delays=0.02/0.01/0/0.45, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 825D6624261)
Jun 13 15:38:32 schnell postfix/smtp: 825D6624261: to=<email@example.com>, relay=none, delay=0.02, delays=0.01/0.01/0/0, dsn=5.4.4, status=bounced (Host or domain name not found. Name service error for name=mail.mydomain.com type=A: Host not found)
So... i USED to have a mailserver at mail.mydomain.com, but have long since removed it. Also, the ZCS server is pointed directly at the authoritative DNS server for the domain for resolution and i've stopped/started all services already to ensure nothing was cached in the resolver library.
Why is it trying to relay to mail.mydomain.com if that host isn't an MX host? it delivers known addresses locally as would be expected, but all the inbound spam that doesn't get caught by amavis is slamming my other server (when i have the DNS A-name re-enabled).