SMTP

SMTP stands for "simple mail transfer protocol" and is the standard for sending emails through the Internet.

SMTP is a relatively simple piece of text-based code in which recipients of an email are specified. That email is sent from a client computer to a server, and then sent on to the recipient. An SMTP client can be found in either the server or the receiving system.

According to Wikipedia's article on SMTP, various forms of electronic messaging were in use as early as the 1960s, but as the government network expanded, it became necessary to employ a new method of emailing between systems on the ARPANET. This gave birth to the first multi-system Internet email protocol.