SMTP Definition (Simple Mail Transfer Protocol)

The Simple Mail Transfer Protocol (SMTP) is a TCP/IP protocol that allows devices to send and receive e-mail.

Compared to other mail transfer protocols, such as POP or IMAP, SMTP is the only protocol that supports sending e-mails from one unknown server to another. However, due to SMTP’s limited ability to queue messages on the receiving end, it is typically used in combination with POP or IMAP.