Fully qualified domain address

A fully qualified domain address (FQDA) is a string forming an Internet e-mail address. It was defined by the Internet Engineering Task Force in RFC 3801 for the use in voice profiles for Internet mail,[1] but has been used on the Internet as early as 1988.

A FQDA is composed of a local part, followed by the symbol @ and the fully qualified domain name (FQDN) of the host responsible for a mailbox.

An example of a FQDA is: localpart@mailhost.example.com. The local part usually denotes a username, while the fully qualified domain name is used by mail transfer agents to determine the IP address of the host by querying the Domain Name System.