(pronounced as separate letters) Short for reverse DNS, a method of name resolution in which an IP address is resolved into a domain name, which is the opposite of the typical resolution method of DNS, which resolves domain names into IP addresses. One practical application of reverse DNS is as an anti-spam measure. Because spammers often use invalid IP addresses to send e-mails, rDNS will determine the authenticity of a domain name compared to the IP address from which it is originating.
