SMTP Simple Mail Transfer Protocol, SMTP, is the language that enables Internet computers to send e-mail to each other. E-mail client software uses the SMTP protocol to send mail to an e-mail server and POP3 or IMAP4 protocols to fetch mail from an e-mail server. When a user sends an e-mail through the Internet, the e-mail client software sends the e-mail to an SMTP server which forwards the e-mail to the destination SMTP server.
