(Electronic-MAIL) The transmission of text messages from sender to recipient. E-mail messages can also be formatted with graphics like a brochure or Web page, an enhancement that many users like, but that creates more spam and a security risk (see HTML e-mail).

Users can send a mail message to a single recipient or to multiple users. In addition, JPEG photos as well as any other type of computer file may be attached to the message (see e-mail attachment). Mail is sent to a simulated mailbox in the organization's mail server until it is downloaded to the "in" mailbox in the user's computer.

The Messaging System and the Client
An e-mail system requires a messaging system, which is primarily a store and forward capability based on the Internet's Simple Mail Transfer Protocol (SMTP). A mail program (e-mail client), such as Outlook for Windows and Mail on the Mac, provides the user interface for mailboxes and send and receive functions. Popular e-mail services such as Gmail and Yahoo! Mail are Web based, in which case the Web browser is used as the mail program (see Internet e-mail service).

The Internet Changed It All
The Internet revolutionized e-mail by turning countless incompatible islands into one global system. Initially serving its own users, in the mid-1990s, the Internet began to act as a mail gateway between the major online services. It then became "the" messaging system for the planet. In the U.S., Internet mail is measured in the trillions of messages each year. To understand the difference between e-mail and fax, see e-mail vs. fax. See messaging system, instant messaging, read receipt and self-destructing e-mail.

The First E-mail on the Internet

In 1971, the first e-mail was typed into the Teletype terminal connected to the Digital Equipment PDP-10 in the rear of the picture below. The message was transmitted via ARPAnet, the progenitor of the Internet, to the PDP-10 in front. Dan Murphy, a Digital engineer, took this photo in the Bolt, Beranek and Newman datacenter. See ARPAnet.