<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (email) transmission . First defined by RFC 821 in 1982, it was updated in 2008 with Extended SMTP additions by RFC 5321, which is the protocol in widespread use today . </P> <P> Although electronic mail servers and other mail transfer agents use SMTP to send and receive mail messages, user - level client mail applications typically use SMTP only for sending messages to a mail server for relaying . For retrieving messages, client applications usually use either IMAP or POP3 . </P> <P> SMTP communication between mail servers uses TCP port 25 . Mail clients on the other hand, often submit the outgoing emails to a mail server on port 587 or 465 . The latter port was previously deprecated, but this changed with RFC 8314 and its use is now recommended to ensure security . SMTP connections on port 25 or 587 can be secured using an extra command (STARTTLS). </P>

What is the role of smtp in email transactions
find me the text answering this question