What is Simple Mail Transfer Protocol (SMTP) ?

 The standard mechanism for electronic mail in the Internet is Simple Mail Transfer

Protocol (SMTP). It provides mail and message exchange between TCP/IP hosts.
SMTP is based on end-to-end delivery i.e., an SMTP client contacts the destination
host’s SMTP server directly for delivering the mail. The destination host’s SMTP
server keeps the mail until the mail has been successfully copied into the recipient’s
SMTP. The SMTP is a connection service based on client-server environment and
runs on port number 25 at the server side as shown in the Figure 8. The various
components of SMTP are:

1) Mail Transfer Agent (MTA)
2) User Agent (UA)