Difference Between SMTP and POP3

To send and receive a mail two agents, message transfer agent and a message access agent are required. The message transfer agent transfers the message from client computer to the recipient’s mail server. Now, it’s the work of message access agent to pull the message from the mailbox present on the mail server at recipient’s side to the recipient’s computer. We have one message transfer agent i.e. SMTP (Simple Mail Transfer Agent), and we have two message access agents  POP (Post Office Protocol) and IMAP (Internet Mail Access Protocol).

What is POP3?
Post Office Protocol version 3 (POP3) is a standard mail protocol used to receive emails from a remote server to a local email client. POP3 allows you to download email messages on your local computer and read them even when you are offline. It is message access agent. It allows to retrieve and organize mails from mailbox on receiver mail server to receiver's computer.

What is SMTP?
Simple Mail Transfer Protocol (SMTP) is the standard protocol for sending emails across the Internet. SMTP uses TCP port 25 or 2525. It is message transfer agent. It transfers the mail from senders computer to the mail box present on receiver's mail server.

The SMTP is a protocol that defines the working of Message Transfer Agent. It is used to send the mail from the sender’s computer to the receiver’s mail server. POP is a pull protocol that is required to pull mail from receiver’s mail server to receiver’s computer.