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.
[citation needed] The earliest email addresses simply had to identify one user from another on one homogenous system, often a single host minicomputer or mainframe.
This worked well only if the first host given in the path was sufficiently well known for the sender's system to be able to contact it.
The modern Internet email address (e.g. john.smith@example.com), is of this type - but it was also used by a number of early systems, including: In this type of system, there is no one unique address for a specific user, but instead a series of attributes, not all of which may be needed to identify the user.
For convenience however, there may be recommended formats for sharing on business cards and similar contexts, such as: