Non-Internet email address

A wide variety of non-Internet email address formats were used in early email systems before the ubiquity of the john.smith@example.com form used by Internet mail systems since the 1980s – and a few are still used in specialised contexts. == Single system == The earliest email addresses simply had to identify one user from another on one homogenous system, often a single host minicomputer or mainframe.

Source: Wikipedia — Non-Internet email address (CC BY-SA 4.0)