Reverse DNS

Internet Standard. Method for systems to resolve an IP address from a domain name. RFC 5855 defines this standard for IPv4 addresses. RFC 8501 defines this standard for IPv6 addresses.

The primary purpose of the Domain Name System (DNS) is to map a domain to an IP address. Some authentication methods want to verify that an IP address belongs to a specific domain. Using Reverse DNS, a recipient server can verify that the given sender's IP address belongs to the domain given in the sender's email address.