Dns – Postfix Reverse DNS Lookup: 450 4.7.1 Client host rejected

dnsemailzimbra

Postfix seems to be consistently rejecting mails from few servers though PTR lookup for those domains is successful. Please see log below. I have run out of ideas on what we can do to get this working. I am sure the issue is not with the sending server as they do not have errors sending to other domains.

Oct 26 09:08:32 mail postfix/smtpd[16158]: NOQUEUE: reject: RCPT from  
unknown[XX.XX.XX.XX]: 450 4.7.1 Client host rejected: cannot find your hostname, 
[XX.XX.XX.XX]; from=<abc@somedomain.com> to=<xyz@mydomain.com> proto=ESMTP 
helo=<somedomain.com>

[root@mail log]# dig -x XX.XX.XX.XX

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 <<>> -x XX.XX.XX.XX
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26837
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 6, ADDITIONAL: 6

;; QUESTION SECTION:
;XX.XX.XX.XX.in-addr.arpa.  IN  PTR

;; ANSWER SECTION:
XX.XX.XX.XX.in-addr.arpa. 7813  IN  PTR somedomain.com.

;; Query time: 417 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Sun Oct 26 09:24:25 2014
;; MSG SIZE  rcvd: 66

Best Answer

Can't 100% answer since you anonamized the data, but Postfix is looking for the PTR and A records to match, as well as the hostname the mail server is claiming to be which looks to be "somedomain.com" from the HELO command in your obfuscated log message.

These are controlled by:

reject_unknown_sender_domain
reject_unknown_client_hostname
reject_invalid_helo_hostname

Postfix Config Params http://www.postfix.org/postconf.5.html

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