E-Mail in the Internet is addressed to a user or other named facility
at a host using a two part address of the form: <user or
facility>@<host>, where host is identified by a domain name (see
Domains, below).
For the purposes of E-Mail a host may be a true internet host with an assigned set of IP addresses, a non-internet host searched through a gateway with an assigned set of IP addresses or a provider host covering all users on an organization (e.g. dec.com, apple.com, ssw.com, hp.com, etc.) serviced by a directory host with an assigned set of IP addresses.