The last component of the address is called the domain of the host computer. Domains are assigned based upon the type of organization that owns the computer. In addition to a domain name, a valid host address must contain at least one subdomain name. The subdomain further specifies the institution that owns the host machine. The subdomain may refer to a specific part of the institution's computer network, or may refer to a specific machine.
User agents are the programs that users interact with to send and read their messages.
Delivery agents work behind the scenes, delivering mail on behalf of the user agents. You will proabably never have to directly interact with delivery agent software. User agents User agents are the programs that allow people to perform all the functions of electronic mail, including reading and sending messages. Some common user agent programs are elm, pine, and pegasus mail. To find out more about the user agents available here at Idaho State University, consult the information on local email software .