Simple Mail Transfer Protocol

The Simple Mail Transfer Protocol, sometimes known as SMTP, is a communication protocol that is an Internet standard for the sending of electronic mail. The Simple Mail Transfer Protocol (SMTP) is used by mail servers and other message transfer agents to send and receive email messages. According to RFC 8314, user-level email clients normally exclusively utilise SMTP for the purpose of sending messages to a mail server for the purpose of relaying. These clients typically submit outgoing email to the mail server on port 587 or 465. When it comes to retrieving messages, the industry standard is IMAP, which succeeded the earlier POP3 protocol. Nevertheless, proprietary servers often incorporate proprietary protocols as well, such as Exchange ActiveSync.

The first iteration of SMTP was developed in 1980, expanding upon ideas that had been used on the ARPANET since 1971. It has undergone a number of revisions, including updates, modifications, and expansions. The version of the protocol that is now in widespread usage has a flexible framework with a variety of extensions for authenticating users, encrypting data, transferring binary data, and internationalising email addresses. Transmission Control Protocol (TCP) is often used by SMTP servers on port number 25 (for plaintext) and port number 587 (for encrypted communications).