The inventor told a colleague not to tell anyone, because it was not what they were supposed to be working on.
In late 1971, Ray Tomlinson, an engineer at Bolt, Beranek and Newman in Cambridge, Massachusetts, sent a test message between two computers sitting side by side in his office.1 Both machines were connected to ARPANET, the Department of Defense research network that linked fifteen computers across the country. Tomlinson had modified an existing program called SNDMSG, which allowed users on the same machine to leave messages for one another, by merging it with CPYNET, a file transfer protocol.2
The test message was something like QWERTYUIOP, the top row of a keyboard. Tomlinson later said he could not remember the exact contents because the message was not meant to be memorable. Nobody had asked him to build the system.
To direct a message to the right person on the right machine, Tomlinson chose the @ symbol to separate the username from the host name.3 Every email address in the world still follows the format he chose that year. Within two years, email accounted for the majority of traffic on ARPANET.4
In 1978, Gary Thuerk, a marketer at Digital Equipment Corporation, sent the first unsolicited commercial email to several hundred ARPANET users promoting a new product.
Queen Elizabeth II sent an email over ARPANET on March 26, 1976, becoming the first head of state to do so.5 The term "e-mail" entered written English around 1979, eight years after Tomlinson's first message.
By the early 1990s, email had migrated from government and academic networks to the commercial internet. The number of active email accounts worldwide now exceeds five billion. Tomlinson was inducted into the Internet Hall of Fame in 2012 and died on March 5, 2016, at the age of seventy-four.6