E-mail is a digital message sent through a computer network from one computer or computer user to another. Early e-mail systems were often specific to a particular network. As of 2006, almost all e-mail is sent via the Internet, or at least uses standard Internet mail protocols so that it can cross the Internet if the sender and receiver are on different networks.
An Internet e-mail address consists of a string of the form [email protected] typically read as "John at server dot net". The first portion is called the "username" and typically indentifies the individual mailbox (which is often but not always associated with a particular user or account) to which the mail is addressed. The second part (after the @-sign) is the domain name and identifies the organization, network, or group of e-mail addresses to which the mail is addressed. The username has meaning only in relation to the domain name. The domain name may consist of a series of names, separated by periods. The username may consist of any strucure at all, and the specific meaning is assigned only by the domain involved.
Primarily e-mail consists of text. But e-mail can also be used to transmit digital images or other computer files. Some e-mail systems allow fonts, colors, and other formatting to be applied to the text of e-mail messages. These systems must transmit the formatting via HTML, or some other format beyond simple text.