Acronym. Simple Mail Transfer Protocol.
Simple Mail Transfer Protocol (SMTP) is an Internet standard for email transmission. It is a connection-oriented, text-based protocol in which a mail sender communicates with a mail receiver by issuing command strings and supplying data over a reliable ordered data stream channel, typically a Transmission Control Protocol (TCP) connection. Per Wikipedia, an SMTP session consists of commands originated by an SMTP client (the initiating agent, sender, or transmitter) and corresponding responses from the SMTP server (the listening agent, or receiver) so that the session is opened, and session parameters are exchanged.
For more information, see:
- Simple Mail Transfer Protocol on Wikipedia