Reverse DNS: The Secret Behind Email Marketing Deliverability

There are many security measures that your domain needs to pass in order for your emails to reach your clients’ inboxes. Reverse DNS is the biggest deliverability killer, as almost all mail servers use this method to verify incoming domains. We are going to show you how to set up reverse DNS in just 5 steps with DNS Made Easy.

What is Reverse DNS?

Reverse DNS is exactly what it sounds like. It’s like a traditional DNS lookup, but backwards. Whenever you enter a website into your browser, you’re actually searching for the IP address of that domain. You can learn more about that here. Reverse DNS takes an IP address and looks for the domain it maps to.

reverse DNS

But why would you ever have an IP address and not the domain name? Well, you wouldn’t, because reverse DNS is used almost exclusively by mail servers. Mail servers use reverse DNS to perform simple anti-spam checks. We like to call this a “three-way handshake”, because mail servers will make sure the forward DNS lookup matches the reverse DNS lookup which matches the fully qualified domain name (FQDN) of the email header.

mail server three way handshake

Setup Reverse DNS

Step 1

First, find your IP address using a command line tool:

$ host [yourdomain.com]

Step 2

We are going to use this address to find out who owns your IP Netblock. A Netblock is the range of IP addresses that your addresses are in. These blocks are usually owned by your ISP (Internet Service Provider). You can find out who owns your block by running a quick WHOIS search. Enter the IP address we got in step 1 into the ARIN lookup tool. The answer will show the NetRange (or IP Netblock) that your address is in and the organization that owns your address.

ARIN whois lookup

Step 3

You will need to ask the provider we identified in step 2 to delegate your IP block to your DNS provider’s name servers. Usually, an ISP or hosting company will only delegate the reverse DNS if you have 256 IPs (a full class C) or more, but some companies have been known to make an exception. If your provider will not delegate the reverse DNS to DNS Made Easy, then you will have to set up your reverse DNS with that provider.

Step 4

If your provider agrees to delegate your IP block to another provider, you will need to ask them for the zone name for your block. This is a special zone (domain) that ends with “in-addr.arpa”. You will need to add this domain to DNS Made Easy, just like you add any other domain.

Important! You must create your domain within DNS Made Easy using the exact same syntax your ISP or hosting provider used to delegate it.

Step 5

Once your domain is set up, you will want to create a PTR record (pointer record) under your reverse DNS domain that points your IP address to your hostname. The full tutorial for adding a PTR record is available here.

After everything is setup, run a quick dig using command line to verify that your PTR record is working.

$ dig -x [your IP address]

ptr record reverse dns

Originally published at DNS Made Easy News.

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