The @ symbol separates the local part from the domain in an email address.
In an address such as [email protected], “jsmith” is the local part, identifying a mailbox or account, while “example.com” is the domain handled by the recipient's mail system. The @ symbol marks the boundary between those two parts.
Ray Tomlinson popularized this format in 1971 when he enabled messages to travel between different computers on ARPANET. He selected @ because it was available on the keyboard and was not normally used in usernames or TENEX commands.
The domain is used to locate the destination mail server, often through DNS mail-exchange records. The local part can contain letters, numbers, and several permitted symbols, but @ has a special structural role in the standard address format.