Defacta
By:
Defacta

Reverse DNS is not a valid Hostname

October 20, 2016 197 views
Email DNS Ubuntu

Hello,

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

The result of postconf smtpheloname is:

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

Why smtpheloname reply $hotname, that looks strange.

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

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

In main.cf, I have:

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

In /etc/mailname there is mydomain.com

What can I do to fix these warnings?

Thanks,
Vincent.

2 Answers

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

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

The result of http://mxtoolbox.com for this is ok:
SMTP Reverse DNS Mismatch OK - 192.34.XXX.XXX resolves to mydomain.com

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

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