E-mail (electronic mail) is the exchange of computer-stored messages by telecommunication. Messages are encoded in ASCII text, however, you can also send non-text files such as graphic images and sound files as attachments sent in binary streams. E-mail was one of the first uses of the Internet and is still probably the most widely used TCP/IP application. A large percentage of the total traffic over the Internet is e-mail. E-mail can also be exchanged between on-line service users and in networks other than the Internet, both public and private.

Some mailing lists allow you to subscribe by sending a request to the mailing list administrator. A mailing list that is administered automatically is called a list server.

A list server is a program that handles subscription requests for a mailing list and distributes new messages from the list's members to the entire list of subscribers as they occur.

The protocol used for electronic mail in the Internet is called the Simple Mail Transfer Protocol or SMTP. The model is of Message Handling Systems and User agents all talking to each other. Both use same protocol and User programs invoke SMTP to send to a receiver.

The receiver may be a mail relay or actual recipient system.

SMTP Mail address look like this: J.Crowcroft@cs.ucl.ac.uk. The general form of such an address is: User @ Domain

The Domain is as defined in the Domain Name Service (DNS) for hosts implementing SMTP. The DNS Name is translated to an IP address. The sending system merely opens a TCP connection to the site and then talks to the SMTP protocol.