Raymond Samuel Tomlinson was a computer engineer at Bolt Beranek and Newman (BBN), the Cambridge, Massachusetts contractor that built the Interface Message Processors for the ARPANET. He is credited with sending the first electronic mail message between two separate computers over a network, an achievement that grew out of a small experiment rather than a planned project. The Internet Hall of Fame, which inducted him as a Pioneer, describes him as “widely known for inventing network electronic mail, choosing the ’@’ sign in emails to connect the username with the destination address.”
In his own firsthand account, archived from his BBN homepage, Tomlinson explained that he had been working on two programs: SNDMSG, a local utility that let users on the same time-sharing machine leave messages for one another, and CPYNET, an experimental program for copying files between machines over the ARPANET. He realized that CPYNET could append data to a mailbox file just as easily as SNDMSG could, and that the two could be combined so a message could be routed across the network to a mailbox on a different host. The result was the first program that could deliver mail between computers.
The choice of the @ sign came from the practical need to distinguish a local mailbox from one on a remote machine. Tomlinson appended an at sign and the host name to the recipient’s login name, using the @ to indicate that the user was located “at” some other host rather than on the local system. The symbol was a natural pick: it appeared on the keyboard, it was unlikely to occur in anyone’s name, and it carried the literal meaning he wanted. That convention, user-at-host, became the universal shape of email addresses and remains so today.
Tomlinson was characteristically modest about the content of those first transmissions. By his own recollection, the test messages he sent between the two machines were “entirely forgettable,” and the very first was most likely something like QWERTYUIOP, simply whatever his fingers typed across the keyboard. He had no sense at the time that he was creating something historic; he was testing whether the combined program worked.
The work spread quickly. SNDMSG with network mail was distributed and adopted across the ARPANET, and within a few years the community was refining the message format and transport mechanics through the Request for Comments series, work that eventually led to standards such as SMTP. Tomlinson’s contribution was not a formal protocol so much as a demonstration and a convention, but both proved durable: networked email became one of the first and most enduring applications of the internet, and the @ sign he chose is now recognized worldwide.