History of email

The history of email extends over more than 50 years, entailing an evolving set of technologies and standards that culminated in the email systems in use today.
Computer-based mail and messaging became possible with the advent of time-sharing computers in the early 1960s, and 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. Many US universities were part of the ARPANET, which aimed at software portability between its systems. That portability helped make the Simple Mail Transfer Protocol (SMTP) increasingly influential.
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.
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.
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 this to pass messages were soon developed and expanded:
Developers of other early systems developed similar email applications:
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.
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:
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 programme 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 an email 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 email programme, from which many other applications have descended.
ARPANET mail.
Experimental email transfers between separate computer systems began shortly after the creation of the ARPANET in 1969. Ray Tomlinson is generally credited as having sent the first email across a network, initiating the use of the "@" sign to separate the names of the user and the user's machine in 1971, when he sent a message from one Digital Equipment Corporation DEC-10 computer to another DEC-10. The two machines were placed next to each other. Tomlinson's work was quickly adopted across the ARPANET, which significantly increased the popularity of email. Tomlinson is internationally known as the inventor of modern email.
Initially addresses were of the form, "username@hostname" but were extended to "username@host.domain" with the development of the Domain Name System (DNS).
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.
Notable first uses of email.
Queen Elizabeth II sent the first email 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 email 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.