History of email
The history of email entails an evolving set of technologies and standards that culminated in the email systems in use today. Computer-based messaging between users of the same system became possible with the advent of time-sharing in the early 1960s, with a notable implementation by MIT's CTSS project in 1965. Informal methods of using shared files to pass messages were soon expanded into the first mail systems. Most developers of early mainframes and minicomputers developed similar, but generally incompatible, mail applications. Over time, a complex web of gateways and routing systems linked many of  them. Some systems also supported a form of instant messaging, where sender and receiver needed to be online simultaneously. 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. Several other email networks developed in the 1970s and expanded subsequently. Proprietary electronic email systems began to emerge in the 1970s and early 1980s. IBM developed a primitive in-house solution for office automation over the period 1970–1972, and replaced  it with OFS (Office System), proving mail transfer between individuals, in 1974. This system developed into IBM Profs, which was available on request to customers before being released commercially in 1981. CompuServe began offering electronic mail designed for intraoffice memos in 1978. The development team for the Xerox Star began using electronic mail in the late 1970s. Development work on DEC's ALL-IN-1 system began in 1977 and was released in 1982. Hewlett-Packard launched HPMAIL (later HP DeskManager) in 1982, which became the world's largest selling email system. The Simple Mail Transfer Protocol (SMTP) protocol 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. During the 1980s and 1990s, use of email became common in business, government, universities, and defense/military industries. Starting with  the advent of webmail (the web-era form of email) and email clients in the mid-1990s, use of email began to extend to the rest of the public. By the 2000s, email had gained ubiquitous status. The popularity of smartphones since the 2010s has enabled instant access to emails. Precursors. The first electrical transmission of messages began in the 19th century in the form of the electrical telegraph, which started to replace earlier forms of telegraphy from the 1840s in the United Kingdom and the United States. Telex became an operational teleprinter service in 1933, beginning in Germany and Europe , and after 1945 spread around the world. The AUTODIN military network in the United States, first operational in 1962, provided a message service between 1,350 terminals, handling 30 million messages per month, with an average message length of approximately 3,000 characters. By 1968, AUTODIN linked more than 300 sites in several countries. Terminology and usage. The term "mail" in the context of messages between computer users has been in use since the 1960s. In RFCs relating to the ARPANET, "network mail" was used since 1973. Historically, the term "electronic mail" is any electronic document transmission. For example, several writers in  the early 1970s used the term to refer to fax document transmission. The Oxford English Dictionary (OED) has a first quotation for "electronic mail" in the modern context in 1975. Electronic mail was widely discussed in the late 1970s, but was usually shortened simply to "mail." In September 1976, a Business Week article entitled "When interoffice mail goes electronic" remarked "In a sense, electronic mail is not new". The OED provides a June 1979 first usage for "E-mail": “Postal Service pushes ahead with E-mail” in the journal "Electronics". No earlier usage has been found; although, the first usage  of the term email may be lost. CompuServe rebranded its electronic mail service as "EMAIL" in April 1981, which popularized the term. The term "computer mail" was also used in the early 1980s. The June 1979 usage of "E-mail" referred to the United States Postal Service (USPS) project called Electronic Computer Originated Mail, which they abbreviated E-COM. USPS began looking into electronic mail in 1977 resulting in the E-COM proposal in September 1978. The service launched in 1982, allowing corporate customers to send electronic mail to a post office branch from where it was printed and delivered  in the normal way, and operated until 1985. Host-based mail systems. With the introduction of MIT's Compatible Time-Sharing System (CTSS) in 1961, for the first time multiple users could log into a central system from remote terminals, and store and share files on the central disk. Informal methods of using such shared files to pass messages were soon developed and expanded into the first mail systems. LAN email systems. In the early 1980s, networked personal computers on LANs became increasingly important. Server-based systems similar to the earlier mainframe systems were developed. Examples include: Eventually these systems  could link different organizations as long as each organization ran the same email system and proprietary protocol. Many providers of mail server software emerged in the 1980s with various features. Email networks. To facilitate electronic mail exchange between remote sites and with other organizations, telecommunication links, such as dialup modems or leased lines, provided means to transport email globally, creating local and global networks. This was challenging for a number of reasons, including the widely different email address formats in use. Attempts at interoperability. Early interoperability among independent systems included: ARPANET mail. Experimental message transfers between separate computer systems began  shortly after the creation of the ARPANET in 1969. Ray Tomlinson, of BBN, sent the first message across the network in 1971, initiating the use of the "@" sign to separate the names of the user and the user's machine. He sent a message from one Digital Equipment Corporation PDP-10 computer to another PDP-10. The two machines were placed next to each other. Tomlinson's work was adopted across the ARPANET, which significantly increased network traffic. Tomlinson is internationally known as the inventor of modern email. From SNDMSG to MSG. In the early 1970s, Ray Tomlinson updated an existing utility  called SNDMSG so that it could copy messages (as files) over the network. Lawrence Roberts, the project manager for the ARPANET development, took the idea of READMAIL, which dumped all "recent" messages onto the user's terminal, and wrote a program for TENEX in TECO macros called "RD", which permitted access to individual messages. Barry Wessler then updated RD and called it "NRD". Marty Yonke rewrote NRD to include reading, access to SNDMSG for sending, and a help system, and called the utility "WRD", which was later known as "BANANARD". John Vittal then updated this version to include three important  commands: "Move" (combined save/delete command), "Answer" (determined to whom a reply should be sent) and "Forward" (sent a message to a person who was not already a recipient). The system was called "MSG". With inclusion of these features, MSG is considered to be the first integrated modern electronic mail program, from which many other applications have descended. FTP mail. Mail on the ARPANET was implemented using the File Transfer Protocol (FTP). Two FTP commands, MAIL and MLFL, permitted an FTP user process to deliver a file or string of text to an FTP server process, designating it as mail  to be made available to a user, identified by a local name, in its host. A "Mail Protocol" was proposed in in July 1971, and a more comprehensive approach in in June 1973, but these were not implemented. The use of the File Transfer Protocol (FTP) for "network mail" was proposed in in March 1973. Through , , , and finally in November 1977, a standardized framework was developed for "electronic mail" using FTP mail servers on the ARPANET. Delivermail was introduced in 1979 as a mail transport agent, i.e. email server. It used the FTP protocol to transmit electronic mail messages to  the recipient. Initially, addresses were of the form, . Addresses were extended to by in February 1982. SMTP. In September 1980, Jon Postel and Suzanne Sluizer published which proposed the Mail Transfer Protocol to implement "computer mail", as a replacement of the use of FTP for mail. of May 1981 removed all references to FTP. In November 1981, Postel published describing the Simple Mail Transfer Protocol (SMTP) protocol, which was updated by in August 1982. After ARPANET switched to TCP/IP in 1982, a new mail transfer agent based on SMTP, Sendmail, was introduced in 1983. After the introduction of the  Domain Name System (DNS) in 1985, mail routing was updated in January 1986 by . As the influence of the ARPANET spread across academic communities, gateways were developed to pass mail to and from other networks such as CSNET, JANET, BITNET, X.400, and FidoNet. This often involved addresses such as: which routes mail to a user with a "bang path" address at a UUCP host. Email clients. During the 1980s and 1990s, use of email became common in business, government, universities, and defense/military industries. Starting with the advent of webmail (the web-era form of email) and email clients in  the mid-1990s, use of email began to extend to the rest of the public. By the 2000s, email had gained ubiquitous status. The popularity of smartphones since the 2010s has enabled instant access to emails. Notable first uses of email. Queen Elizabeth II sent the first electronic mail from a head of state over the ARPANET from the Royal Signals and Radar Establishment in England on March 26, 1976. Jimmy Carter's presidential campaign became the first to use electronic mail for internal communications in the autumn of 1976. IBM PROFS email was used by the U.S. National Security Council  under President Ronald Reagan in the 1980s. The first U.S. president to use Internet email was Bill Clinton in the 1990s, including a reply to an email from the prime minister of Sweden in 1994.