Electronic mail (usually shortened to email; alternatively hyphenated e-mail) is a method of transmitting and receiving digital messages using electronic devices over a computer network. It was conceived in the late–20th century as the digital version of, or counterpart to, mail (hence e- + mail). Email is a ubiquitous and very widely used communication medium; in current use, an email address (commonly local-part + @ + domain name) is often treated as a basic and necessary part of many processes in business, commerce, government, education, entertainment, and other spheres of daily life in most countries.
Email operates across computer networks, primarily the Internet, and also local area networks. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver, and store messages. Neither the users nor their computers are required to be online simultaneously; they need to connect, typically to a mail server or a webmail interface to send or receive messages or download it.
Originally a text-only ASCII communications medium, Internet email was extended by MIME to carry text in expanded character sets and multimedia content such as images. International email, with internationalized email addresses using UTF-8, is standardized but not widely adopted.
The term electronic mail has been in use with its modern meaning since 1975, and variations of the shorter E-mail have been in use since 1979:
email is now the common form, and recommended by style guides. It is the form required by IETF Requests for Comments (RFC) and working groups. This spelling also appears in most dictionaries.
e-mail was originally the form favored in edited published American English and British English writing, and was formerly preferred by some style guides.
E-mail is sometimes used. The original usage in June 1979 occurred in the journal Electronics in reference to the United States Postal Service initiative called E-COM, which was developed in the late 1970s and operated in the early 1980s.
EMAIL was used by CompuServe starting in April 1981, which popularized the term.
EMail is a traditional form used in RFCs for the "Author's Address".
The service is often simply referred to as mail, and a single piece of electronic mail is called a message. The conventions for fields within emails—the "To", "From", "CC", "BCC" etc.—began with RFC-680 in 1975.
An Internet email consists of an envelope — the header of the message which contains the 'From' address, 'Recipient'address, network routing information, etc., and content — the body of the message itself.
Computer-based messaging between users of the same system became possible after the advent of time-sharing in the early 1960s, with a notable implementation by MIT's CTSS project in 1965. Most developers of early mainframes and minicomputers developed similar, but generally incompatible, mail applications. In 1971 the first ARPANET network mail was sent, introducing the now-familiar address syntax with the '@' symbol designating the user's system address. Over a series of RFCs, conventions were refined for sending mail messages over the File Transfer Protocol.
Proprietary electronic mail systems soon began to emerge. IBM, CompuServe and Xerox used in-house mail systems in the 1970s; CompuServe sold a commercial intraoffice mail product in 1978 to IBM and to Xerox from 1981. DEC's ALL-IN-1 and Hewlett-Packard's HPMAIL (later HP DeskManager) were released in 1982; development work on the former began in the late 1970s and the latter became the world's largest selling email system.
The Simple Mail Transfer Protocol (SMTP) was implemented on the ARPANET in 1983. LAN email systems emerged in the mid-1980s. For a time in the late 1980s and early 1990s, it seemed likely that either a proprietary commercial system or the X.400 email system, part of the Government Open Systems Interconnection Profile (GOSIP), would predominate. However, once the final restrictions on carrying commercial traffic over the Internet ended in 1995, a combination of factors made the current Internet suite of SMTP, POP3 and IMAP email protocols the standard (see Protocol Wars).
The following is a typical sequence of events that takes place when sender Alice transmits a message using a mail user agent (MUA) addressed to the email address of the recipient.
The MUA formats the message in email format and uses the submission protocol, a profile of the Simple Mail Transfer Protocol (SMTP), to send the message content to the local mail submission agent (MSA), in this case smtp.a.org.
The MSA determines the destination address provided in the SMTP protocol (not from the message header)—in this case, bob@b.org—which is a fully qualified domain address (FQDA). The part before the @ sign is the local part of the address, often the username of the recipient, and the part after the @ sign is a domain name. The MSA resolves a domain name to determine the fully qualified domain name of the mail server in the Domain Name System (DNS).
The DNS server for the domain b.org (ns.b.org) responds with any MX records listing the mail exchange servers for that domain, in this case mx.b.org, a message transfer agent (MTA) server run by the recipient's ISP.