Introduction into SMTP ********************** SMTP (Simple Mail Transfer Protocol) is a communication protocol for electronic mail transmission. As an internet standard, SMTP is primarily used by mail servers and other message transfer agents to send and receive mail messages. User-level client mail applications typically use SMTP only for sending messages to a mail server for relaying. While SMTP is used for the transmission of emails, protocols like IMAP or POP3 are traditionally used to retrieve them. If you are looking for a complete email integration that also includes IMAP or POP3 retrieval functionalities, you should also take a look at the `balderhub-mail `_ package. This package builds upon SMTP and provides comprehensive features for handling both sending and receiving of emails. In the context of the ``balderhub-smtp`` package, the focus is entirely on providing and utilizing SMTP functionalities, making it ideal for testing simple mail transmission and simulating an SMTP server. SMTP was first defined in 1982 by `RFC 821 `_, and last updated in 2008 by `RFC 5321 `_ to Extended SMTP additions, which is the protocol variety in widespread use today. Mail servers use SMTP to send, receive, and relay outgoing mail between email senders and receivers. .. note:: Coming more soon.