KB06051001 Reverse DNS

What is Reverse DNS?

Reverse DNS (rDNS) associates a given IP address with a specific domain, using the Pointer or PTR record. 
Reverse DNS is used to authenticate an address with the domain.  

For example, it might turn 192.0.2.25 (IP address) into example.mysite.com (hostname / domain name). rDNS does this by looking at the PTR record of the IP address in question and resolving it to a hostname based on the settings configured by a mail administrator - this is the domain name set in the Mailtraq Console at Options | Server

It is used by many email servers to reduce spam by rejecting messages that do not have a valid Reverse DNS entry.

Do I need a reverse DNS entry?

The RFCs say you should have a reverse DNS for all your mail servers. It is recommended that you have them, as many mailservers will not accept mail from mailservers with no reverse DNS entry. 

If your mail server does not have a PTR record set up to associate the IP address with the domain name, it will fail the rDNS test and may not be able to send email to other mail servers.

How do I get a Reverse DNS entry?

This is not a setting inside Mailtraq: your ISP or Internet connectivity provider must create the PTR record for you. Contact Technical Support at your ISP and request they set up a PTR record to associate your domain name with your IP address.

Where can I find out more?

There are easy to follow articles about this topic at Wikipedia here