Forward Confirmed RDNS

One of the problems with spam filtering is to make sure your good outgoing email doesn't get blocked by other people's spam filters. To do that, you have to make your email servers appear as clean as possible. One way to do that is to get your reverse DNS (rDNS) correct. And it's not as easy as you might think.

There are basically two steps to getting rDNS correct. You have to create a PTR record for the IP address, and you have to make sure that the name returned by the PTR record actually points back to the original IP address. This is what is called Forward Confirmed rDNS.

For example, if your email server is on IP 1.2.3.4, then you set a PTR record to point to your email server mail.example.com. And you make sure that mail.example.com points back to 1.2.3.4.

1.2.3.4 -> mail.example.com
mail.example.com -> 1.2.3.4

External resources

• Forward Confirmed RDNS - Detailed explanation
• FCrDNS Tester - Test your RDNS to see if it's correct!