Origin

E-mail predates the inception of the Internet, and was in fact a crucial tool in creating the Internet.

MIT first demonstrated the Compatible Time-Sharing System (CTSS) in 1961. It allowed multiple users to log into the IBM 7094 from remote dial-up terminals, and to store files online on disk. This new ability encouraged users to share information in new ways. E-mail started in 1965 as a way for multiple users of a time-sharing mainframe computer to communicate. Although the exact history is murky, among the first systems to have such a facility were SDC's Q32 and MIT's CTSS.

E-mail was quickly extended to become network e-mail, allowing users to pass messages between different computers by 1966 or earlier (it is possible that the SAGE system had something similar some time before).

The ARPANET computer network made a large contribution to the development of e-mail. There is one report that indicates experimental inter-system e-mail transfers began shortly after its creation in 1969. Ray Tomlinson initiated the use of the "@" sign to separate the names of the user and their machine in 1971.^[18] The ARPANET significantly increased the popularity of e-mail, and it became the killer app of the ARPANET.

Most other networks had their own email protocols and address formats; as the influence of the ARPANET and later the Internet grew, central sites often hosted email gateways that passed mail between the Internet and these other networks. Internet email addressing is still complicated by the need to handle mail destined for these older networks. Some well-known examples of these were UUCP (mostly Unix computers), BITNET (mostly IBM and VAX mainframes at universities), FidoNet (personal computers), and DECNET (various networks).

An example of an Internet email address that routed mail to a user at a UUCP host:

hubhost!middlehost!edgehost!user@uucpgateway.somedomain.example.com

This was necessary because in early years UUCP computers did not maintain (or consult servers for) information about the location of all hosts they exchanged mail with, but rather only knew how to communicate with a few network neighbors; email messages (and other data such as Usenet News) were passed along in a chain among hosts who had explicitly agreed to share data with each other.