Ray Tomlinson

Two TENEX machines, side by side

In late 1971, at Bolt Beranek and Newman in Cambridge, Massachusetts, Ray Tomlinson modified the TENEX program SNDMSG with code lifted from the experimental file-transfer program CPYNET, so it could append a message to a mailbox on another ARPANET host.

He tested it by sending to himself between two TENEX computers that stood next to each other but whose only computer-to-computer link ran through the ARPANET. The work came to roughly 400 added lines of assembly and, by his own estimate, three or four working days spread over a couple of weeks.

Why the date stays vague

Tomlinson consistently dated the tests only to “late 1971.” No surviving record fixes a day or a month, which is why the entry belongs at year-level precision.

The content of the first successful message is unknown too. He sent many partial and complete tests and could not say which one first crossed intact; “QWERTYUIOP” was his example of the sort of meaningless string he might have typed, not a preserved quotation.

The @ sign, and what “first” means here

Tomlinson introduced the user@host form, picking “@” because it read as a user being located “at” another machine. He did not invent the character; he repurposed one already on the keyboard.

Nor did he invent electronic mail. Messaging between users of a single computer existed years earlier — SNDMSG itself was one such program — so the claim holds only for mail between users on different hosts.

Once the tests worked he used the new system to tell his colleagues how to send network mail, and the capability shipped to other TENEX sites in the next release in early 1972.