Reverse DNS

Reverse DNS is the process of resolving an IP Address to a Domain Name. The usual DNS process involves the opposite; resolving a Domain Name to an IP Address. Usually, when you want to visit a website such as www.emergecore.com, you type that URL into the address space in your web browser. Your browser will then contact the DNS servers on the Internet and request that the name be resolved to the IP Address. Your browser will then use that address to connect to the website and download the page. Reverse DNS does the opposite and has typically been used to thwart spam mail delivery. Spammers typically use a spoofed or an invalid IP address that does not match the domain name they are referencing. One defense has been for mail servers on the Internet to request a Reverse DNS Lookup so they can determine the validity of the IP address the spam mail was coming from. If the reverse lookup failed, the mail was rejected. This can also sometimes result in legitimate mail not being delivered. For more information, see the terms Domain, DNS, IP Address, MX Record, and NS Record in this Glossary.