Ray Tomlinson chose the @ symbol to separate user and host names in email addresses.
In 1971, Tomlinson was working on ARPANET, the network that preceded today’s Internet. Existing electronic mail programs could send messages only between users on the same computer. Tomlinson adapted the system so mail could travel between different networked hosts, creating the familiar user@host structure.
He selected @ because it was already available on keyboards but was uncommon in usernames and programming conventions. Its meaning also made intuitive sense: the user was “at” a particular host. The choice distinguished the recipient’s local account from the destination machine without adding ambiguity.
The first network email message was not preserved, and Tomlinson later said its content was probably an unimportant random string. The @ sign, however, endured and became one of the defining symbols of digital communication. It is also an older commercial and accounting symbol, not one invented for email.