What is Reverse DNS?
When you need someone’s phone number you go to your phone’s contact list and you search for it. This is pretty much how Domain Name System, or DNS, works. In order to connect you to a specific website you’re looking for, DNS takes the domain name and confirms the IP address of that domain to connect you to the correct page.
But let’s say you’re searching for your contact list by address instead of name. This is the same idea behind a rDNS lookup. Reverse DNS is when you look up the internet host by their IP address and it then uses that address to connect you to the page. In other words, a reverse DNS or reverse IP lookup will allow you to start with an IP address instead of the domain name.
For example, a regular DNS search, known as a ‘forward DNS’ would be asking, “What’s the address of msn.com? The DNS server would confirm that the IP of msn.com is 184.108.40.206. A rDNS search would do the opposite. So we would ask DNS to lookup the domain for the IP 220.127.116.11 and it would confirm that it belongs to msn.com.
Why is Reverse DNS important?
You’re probably wondering why should you care about rDNS. The main reason it’s so important boils down to one thing: email deliverability. Simply put, without rDNS your emails will be blocked.
To put this into perspective, follow along with this example.
You compose and attempt to send an email to someone at johndoe@somedomain. What happens next is your computer completes a rDNS lookup to verify the receiver. After all, you want your email going to johndoe@somedomain and not someone else, right?
Your computer finds that the IP address for somedomain.com is 18.104.22.168. But now, it has to go a step further as it should It now asks, “What is the domain of the computer located at 22.214.171.124?” The answer should be that the computer located at 126.96.36.199 is known as somedomain.com, and if it is, your email would be sent. However, if it comes back that the domain of that IP address is really someotherdomain.com, that email will be blocked. Now if it comes back that it doesn’t know what your IP address is commonly known as because that person didn’t have reverse DNS setup, then for sure, it will be blocked.
If you don’t have rDNS, you will have a low deliverability rate for both incoming and outgoing emails. Needless to say, this can be a big issue for people running businesses or websites.
Knowing about rDNS or reverse IP is good, but understanding how it affects you is even more important. Now that you understand why it should matter to you and how it may affect your business, it’s time to get proactive. Ensure that you have rDNS setup so that your IP is whitelisted and your deliverability rate is increased.