Simple Mail Transfer Protocol (SMTP) is a protocol which handles sending e-mail and routing e-mail between mail servers .And with the help of smtp we can provides smtplib module which defines an SMTP client session object that can be used to send mail to any Internet machine with an SMTP or ESMTP listener daemon.
For example you can see below code-

import smtplib
smtpObj = smtplib.SMTP( [host [, port [, local_hostname]]] )

Here is the detail of the parameters:
host: This is the host running your SMTP server. You can specify IP address of the host or a domain name like Findnerd.com. This is optional argument.
port: If you are providing host argument, then you need to specify a port, where SMTP server is listening. Usually this port would be 25.
local_hostname: If your SMTP server is running on your local machine, then you can specify just localhost as of this option.