What does SMTP stand for?

SMTP stands for Simple Mail Transfer Protocol. It is the standard application-layer protocol used to send email between mail servers and to submit outgoing messages from an email client to a mail server.

SMTP grew out of early ARPANET email systems and was standardized in the early 1980s. It uses a store-and-forward model: a sending server transfers a message to the recipient's server, which can then deliver it to the recipient's mailbox. SMTP defines how mail is transported, including sender and recipient commands, but the message's headers and body are specified by separate Internet mail standards.

SMTP is often confused with the protocols used to retrieve email. IMAP and POP are commonly used by email applications to access stored messages, while SMTP handles sending and relaying. Modern deployments commonly use port 587 for authenticated submission, port 25 for server-to-server transfer, and port 465 for encrypted submission.