The invention of email as we know it today is credited to Ray Tomlinson in 1972. However, email has been used since the early 1960s. The main difference between this early email system and Tomlinson's is that the former only allowed users who shared a computer to message each other.
When computers started being connected to each other in networks, a method to send messages to other computers needed to be devised. Tomlinson chose to use the @ symbol — already available on computer keyboards — after a username to indicate to which network computer the message should be sent.