SMTP

SMTP (Simple Mail Transfer Protocol) is an Internet standard for email transmission. Created by Jon Postel in 1982, SMTP is used to send and receive email messages between servers. It operates at the application layer of the Internet protocol suite and uses port 25 by default.

SMTP is the primary protocol used for sending electronic mail on the Internet. Established by Jon Postel and documented as RFC 821 in 1982, it was one of the early protocols adopted by the ARPANET. SMTP is designed to enable the reliable and efficient transmission of emails between servers. The protocol works by establishing a connection to the recipient's email server and then transferring the message data. By default, SMTP uses port 25, although ports 587 and 465 are also commonly used for secure transmission via TLS/SSL. SMTP only covers sending and relaying of messages; clients normally receive email using different protocols such as POP3 or IMAP. This protocol remains foundational to modern email communication, ensuring that messages are correctly routed from the sender to the recipient.