What is "smtp"
SMTP was first defined by RFC 821 in the year 1982 and had its last update defined in RFC 5321 (in 2008) which includes additions to extended SMTP (ESMTP) and is a widely used protocol today. The SMTP is specified for outgoing email transport and uses TCP port 25. The protocol for new shipments is for all purposes the same as SMTP, but uses port 587. Secure SMTP connections over SSL are known by the acronym SMTPS, although SMTPS is not a protocol per se.
While email servers and other message transfer agents use SMTP to receive and send messages, email client applications for the end user typically use SMTP only to send emails to a mail server re-lay (repeat). To receive messages, client applications typically use POP protocols (Post Office Protocol), IMAP (Internet Message Access Protocol) or proprietary systems (such as Microsoft Exchange or Lotus Notes/Domino) to access your email accounts on an email server.