What is the difference between SMTP and POP3?
SMTP is a service which resides on port 25 & which is responsible for sending & receiving mails.
POP however is a service which is responsible for the delivery of mails to the mail client for eg MS outlook Express . POP server resides on port 110 .
The email server comprises of two services--one to receive and another to send.
POP3(Post Office Protocol version 3) is for downloading mails.It works like regular post office. Mails come and reside in your mail box till you download.
The latest standard is IMAP and it works differently.
SMTP is for out-going mail.
These are two widely used protocols for e-mail distribution and each has its own purpose. SMTP (Simple Mail Tranfer or Transport Protocol) is used for delivering the mail (that you "send") to the intended recipient. POP3 (Post Office Protocol 3) is used to "pull" mails from your mail server (which stores incoming mails) into the your mail client (e.g., Outlook Express).