How to use rDNS (Reverse DNS)
Posted by Gary, Last modified by on 27 May 2008 06:03 PM


Reverse DNS is another way of fighting spam. It allows other servers to check the authenticity of your server.

How to

  1. You will need to know your IP address. You can look up your IP address using the ipconfig command within a Windows console


2. Make a note of your IP address. If there are multiple IP addresses listed, then the first one is the one you need.

Go to and enter your IP address after selecting the Reverse Lookup option.

The results beneath will tell you whether you have a reverse DNS entry.


If you do have a reverse entry, use the name of the reverse entry to update the SmartDiscover tab as show in the example below.

Example - for a reverse name of

System > Services > SmartDiscover tab



You will also need to create a DNS record for pointing to this IP address.

If you do not have a reverse entry, you will need to contact your service provider to have one set up.

Further information about rDNS can be found at:

Note: Icewarp can be configured to check other servers for rDNS records. See Mail > Security > DNS tab in the administrator console.