From some of the city and state government email servers, email is being rejected with unknown_host_name error. see message below
My suspicion is if a large organization has multiple email servers, then postfix may just be looking at the nslookup results of the first returned server, see there is not a match and then drop it?
Any thoughts on this? Do I have something configured wrong? Maybe dns not working properly?
found in /var/log/zimbra.log
--- message from logs---
Jan 18 04:14:58 postal3 postfix/smtpd: connect from norfmail.norfolk.gov[220.127.116.11]
Jan 18 04:14:58 postal3 postfix/smtpd: NOQUEUE: reject: RCPT from norfmail.norfolk.gov[18.104.22.168]: 450 <proofpoint2.norfolk.gov>: Helo command rejected: Host not found; from=<email@example.com> to=<firstname.lastname@example.org> proto=SMTP helo=<proofpoint2.norfolk.gov>
Jan 18 04:14:58 postal3 postfix/smtpd: disconnect from norfmail.norfolk.gov[22.214.171.124]
Turn Off The HELO Check
You need to turn off the appropriate DNS/HELO check(s). Postfix is rejecting the mail because the MX record doesn't match the hostname the server announces itself as.
Originally Posted by Ericx
See http://dnsreport.com/tools/dnsreport...in=norfolk.gov for more detail.
Many would say the email admin responsible for norfolk.gov has misconfigured things, but many email systems are configured this way, unfortunately, so we turn these kinds of checks off to avoid "false positives" like the one you are experiencing.
The bad news is that rejecting spam via HELO and DNS checks--before they hit the Postfix mail queues--is very effective. Once we turned these checks off, the volume of messages through the Postfix queues jumped by 400%, and the volume of spam hitting our clients' Inboxes went from 0-3 per day to 3-6 per day.
Such is life...