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May 27, 2014

domain has no valid mail exchangers

Filed under: Linux — Tags: , , , , , — admin @ 8:33 pm

Today I face a strange problem with e-mail won’t be deliver, to a client . I have tested from yahoo, gmail and other service and everything was fine however one client from gmx was complain that he can’t send e-mail to that account

A message that you sent could not be delivered to one or more of
its recipients. This is a permanent error. The following address
failed:

“user@domain.com”:
domain has no valid mail exchangers

So, first impresion was to check if domain.com have a mx . So a short
dig mx domain.com output a

DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 mail.domain.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 0 ;; QUESTION SECTION: ;domain.com. IN MX ;; ANSWER SECTION: domain.com. 2011 IN MX 10 mail.domain.com.

So it appear that is there.
But the problem was when I query to see who is the mail.domain.com

dig mail.domain.com

DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 mail.domain.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 0 ;; QUESTION SECTION: ;mail.domain.com. IN A ;; ANSWER SECTION: mail.domain.com. 1937 IN CNAME domain.com. domain.com. 1937 IN A xxx.xxx.xxx.xx ;; AUTHORITY SECTION: domain.com. 1932 IN NS dns1.domain.com. domain.com. 1932 IN NS dns2.domain.com. ;; Query time: 3 msec

So we see that mail.domain.com is a CNAME, it appear that is against rfc , and need to be A zone and not alias/CNAME.
So the solution is to modify mail.domain.com to be A xxx.xxx.xxx.xxx

Regards

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