Reverse DNS is not a valid Hostname

October 20, 2016 2.2k views
Email DNS Ubuntu


I installed postfix with webmin on Ubuntu14 LTS. For the reverse DNS, the name of the droplet is

The result of postconf smtpheloname is:

root@Ubuntu-14LTS-NY1:~# postconf smtp_helo_name
postconf: warning: /etc/postfix/ undefined parameter: mua_sender_restrictions
postconf: warning: /etc/postfix/ undefined parameter: mua_client_restrictions
postconf: warning: /etc/postfix/ undefined parameter: mua_helo_restrictions
smtp_helo_name = $myhostname

Why smtpheloname reply $hotname, that looks strange.

And I have two warnings with [ ](http://)

  • Reverse DNS is not a valid Hostname
  • Reverse DNS does not match SMTP Banner -

In, I have:

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no
myorigin = /etc/mailname
mydestination =, localhost

In /etc/mailname there is

What can I do to fix these warnings?


3 Answers

Make your droplet name a hostname that points back to its IP address.

But the name of the droplet is and it points back to the IP address 192.34.XXX.XXX.

The result of for this is ok:
SMTP Reverse DNS Mismatch OK - 192.34.XXX.XXX resolves to

That's why I think the problem comes from my postfix config, but I am not sure.

I am having this same problem. Did you ever find the solution?

Have another answer? Share your knowledge.