Electronic mail is a method of exchanging digital messages between computer users; Email first entered substantial use in the 1960s and by the 1970s had taken the form now recognised as email.
Email servers accept, forward, deliver, and store messages.
Neither the users nor their computers are required to be online simultaneously; they need to connect only briefly, typically to a mail server, for as long as it takes to send or receive messages.
Originally an ASCII text-only communications medium, Internet email was extended by Multipurpose Internet Mail Extensions (MIME) to carry text in other character sets and multimedia content attachments.
International email, with internationalized email addresses using UTF-8, has been standardized, but as of 2016 not widely adopted.
Autodin was supported by 18 large computerized switches, and was connected to the United States General Services Administration Advanced Record System, which provided similar services to roughly 2,500 terminals.
These original messaging systems had widely different features and ran on systems that were incompatible with each other.
Most of them only allowed communication between users logged into the same host or "mainframe", although there might be hundreds or thousands of users within an organization.
In the early 1980s, networked personal computers on LANs became increasingly important.
The history of modern, global Internet email services reaches back to the early ARPANET, with standards for encoding email messages proposed as early as 1973 (RFC 561).
An email message sent in the early 1970s looks very similar to a basic text email sent today.
Email played an important part in creating the Internet, and the conversion from ARPANET to the Internet in the early 1980s produced the core of the current services.