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[8295]: connect from norfmail.norfolk.gov[216.54.20.203]
Jan 18 04:14:58 postal3 postfix/smtpd[8295]: NOQUEUE: reject: RCPT from norfmail.norfolk.gov[216.54.20.203]: 450 <proofpoint2.norfolk.gov>: Helo command rejected: Host not found; from=<bob.clark@norfolk.gov> to=<zimbra_user@example.com> proto=SMTP helo=<proofpoint2.norfolk.gov>
Jan 18 04:14:58 postal3 postfix/smtpd[8295]: disconnect from norfmail.norfolk.gov[216.54.20.203]