SMTP means Simple Mail Transfer Protocol is a TCP/IP protocol.
It is used in sending and receiving e-mail.
An organized system takes care of your envelope and through a series of steps it drops it off to your recipient.
In this process, the SMTP server is simply a computer running SMTP, and which acts like the postman.
The messages have been picked up once they are sent to this server, which takes care of concretely delivering emails to their recipients.
SMTP language defines only the message’s transmission, and doesn’t deal with its body content.
SMTP uses TCP well known port 25.
The exchange of email using TCP is performed by a Message Transfer Agent (MTA).
An example for MTA for UNIX Operating Systems is Sendmail.
End users normally don’t deal with the MTA.
MTA’s are set by the System Administrators.
The communication between a SMTP client and SMTP server is by human readable ASCII text.
SMTP has advantages such as simplicity,Quick e-mail delivery and reliability.