Reverse IP lookup for email

Posted on Posted in Features, Networking, Routing

What is reserved lookup for email? Well first of all, we will need to understand that in the DNS (Domain Name Service) world there are 2 types of DNS lookup, the first one is the common every day usage that is call “forward lookup” and the second one for advance enterprise grade that is call “reversed lookup”. Let at them in details;

Forward lookup

This type is common one we all use; it’s the system that tells the computer that what IP address this domain name represents. Easy computer need to communication with each other using IP address. But we human don’t use IP addresses like the computer do we (not talking about IPv6 too). We use something that is more memorized able, called “domain name”. Therefore we would need some kind of system to work in the middle be us and the computer, and that is the “forward lookup”

Forward Lookup System

Reversed lookup

This something is similar to forward lookup, but forward lookup is for Domain-to-IP and reversed lookup is for IP-to-Domain translation. Why do we need this? Well email spam and spoofing are being so common these days, so well something that could identify that this email is actually from the owner of the email’s mail server.

Reversed lookup System

How do I check this?

It is easy open your command prompt and firer up “nslookup”, here let check forward lookup

nslookup forward lookup

As you can see, I did a forward lookup on our email server, and the DNS system return me with IP address of domain name. Now let do a reversed lookup on this IP address we found from our return results.

nslookup reversed lookup ok

Cool it’s showing that is IP reversed back to the same domain name. This can true identify that if an email is sent from for example @yourdomain.com email server of 66.231.113.53 and doing a reversed lookup for that IP 66.231.113.53 giving the same domain name. This can true verify that this is from the actual email server of that domain.

Ok what does look like if I don’t have a reversed lookup for my email server here the result;

nslookup forward lookup

Now let’s try doing a reversed check for the IP address

nslookup reversed lookup fail

Aha! This does not identify that I’m from the a reversed lookup setup here, then if the receiving email server does a reversed lookup check on my email sent to him, my email will get rejected by anti-spam reversed lookup check policy.

Here is a print screen of an email header that pass anti-spam reversed lookup policy on my another email server.

Email that pass anti-span reversed lookup policy

Why use reversed lookup?

Well, you don’t want another people trying spoofing as being you and steal your customers identities now would you. Reversed lookup is a mechanism to protect you from this type fraud, also another conscience that you must take that now all businesses are now taking reversed lookup filter out spam emails in their anti-spam policy. Therefore to ensure that your communication via email go through with your partners, especially in the European Union.