The origin of SMTP (and other protocols)

Today's Internet e-mail clients all use SMTP to send mail. Like other Internet protocols, SMTP was initially proposed in a request for comments (RFC) document. RFCs were often accompanied by programs (in this case an SMTP client and server) that implemented the proposed protocol. Users were free to modify and comment on the proposal, and the true test of its success was whether or not they began using the protocol.

If you are wondering where the SMTP commands like helo, send, rctp, data, etc. came from, you only need look at RFC 821 which defined them.

Note that all RFCs were not accepted as is. For example, RFC 821 is a revision of RFC 772 which defined its predecessor, the Mail Transfer Protocol.

You will also notice that the author of these and many other protocols we use today was Jon Postel, one of the central inventors of the Internet.

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