How to configure rDNS in Zimbra ?

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DNS

The reverse DNS resolution (rDNS) is a determination of the domain name that is associated to an IP. Some email companies like AOL, for example, will reject any email that doesn't have a valid rDNS.

Zimbra-rDNS.png

Where needs to be configured?

To have a perfect match between the rDNS and the SMTP Banner of the server, need to have the next:

  • In the public DNS of the ISP provider. Or if you have control of the public DNS of your IP range, then you can add the rDNS by yourself.
  • In the Zimbra Server, need to edit the HELO to match between it and the rDNS record.

How to configure it?

To modify the Public DNS to match the IP and the rDNS, you need to contact with your ISP provider, or if you have acces to edit the DNS record of your IP, then change it by yourself. For example, if you have the IP 60.60.60.60 and needs to resolve to mail.example.com.


To edit the SMTP Banner and match it with the external rDNS. Need to edit the next in Zimbra:


Zimbra 8.0.X 

zmlocalconfig -e postfix_smtpd_banner="mail.example.com"
zmcontrol restart


Zimbra 8.5, 8.6, and above 

zmprov ms  `zmhostname` zimbraMtaSmtpdBanner mail.example.com
zmcontrol restart


Ref:
https://wiki.zimbra.com/wiki/Best_Practices_on_Email_Protection:_SPF,_DKIM_and_DMARC

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