Electronic mail, commonly called email or e-mail, is a method of exchanging digital messages across the Internet or other computer networks. Originally, email was transmitted directly from one user to another computer. This required both computers to be online at the same time, in the same way that instant message systems are now. Today's email systems are based on a store-and-forward model. This means that email servers accept messages, forward them on to the destination server (if necessary), then deliver them to the recipient when they are online.
Users no longer need be online simultaneously and need only connect briefly, typically to an email server, for as long as it takes to send or receive messages. An email message consists of two components, the message header, and the message body, which is the email's content. The message header contains control information, including, minimally, an originator's email address and one or more recipient addresses. Usually additional information is added, such as a subject header field.
Originally, email was a text-only communication medium. It was was later extended to carry multi-media content attachments (eg pictures), which are called Multipurpose Internet Mail Extensions (MIME).Advantages