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). In this article, I have discussed the differences between SMTP and POP3.

The basic difference between SMTP and POP3 is that SMTP is a message transfer agent used to send the message and POP3 is a message access agent used to receive the message. There are some more differences between SMTP and POP3 which I have discussed in the comparison chart shown below; please have a look.

Content: SMTP Vs POP3

1. Comparison Chart
2. Definition
3. Key Differences
4. Conclusion

Comparison Chart

Basis for Comparison	SMTP	POP3
Basic	It is message transfer agent.	It is message access agent.
Full form	Simple Mail Transfer Protocol.	Post Office Protocol version 3.
Implied	Between sender and sender mail server and between sender mail server and receiver mail server.	Between receiver and receiver mail server.
work	It transfers the mail from senders computer to the mail box present on receiver's mail server.	It allows to retrieve and organize mails from mailbox on receiver mail server to receiver's computer.

Definition of SMTP

SMTP (Simple Mail Transfer Protocol) is a Message Transfer Agent (MTA). There are two MTAs client MTA and server MTA. A client MTA at clients system sends mail which is received by the server MTA at client’s mail server. Further, the client mail server has client MTA which sends the mail from client’s mail server to the server MTA at recipient’s mail server.  SMTP is a protocol that defines both client-server MTA, on the internet.

SMTP protocol is used in the scenario where both the sender and receiver of mail must be connected to their mail server by WAN or LAN. SMTP protocol is used two times, first between sender and its mail server and second between client’s mail server and receivers mail server. SMTP is not used between receiver’s mail server and receiver; the POP protocol accomplishes this task.

Now let’s concentrate on the working of SMTP. SMTP defines the command and responses that are used to transfer the messages between client and server MTA. The commands are sent from client to the server. The responses are sent back from the server to the client.

The mail transfer between Client MTA and Server MTA occurs in three phases: Connection establishment, mail transfer, and Connection termination. Initially, the connection is established between client and server MTA. After the connection is established, a single mail is exchanged between the single sender and several recipients. After the successful transfer of the message the connection is terminated by the client.

Definition of POP3

As we have seen above SMTP accomplishes the mail delivery task from client to server MTA. Now a  pull protocol is required to pull the mail from the MTA server to the receiver. For this, we have POP3 protocol i.e. Post Office Protocol version 3. It is message access agent.

The POP3 has client and server MAA; client MAA software is installed on the recipient computer whereas, the server MAA is installed on the recipient’s mail server. To access/read the mail the user has to first download the mail from mailbox on mail server to its computer.

To access mail from the mail box present at the mail server the client MAA at recipient computer establishes the connection with the mail server using TCP port 110. For establishing connection client MAA at recipient’s computer sends username and password to the mailbox. Then the user is authenticated to retrieve mail messages one by one.

POP3 works on two modes delete mode and keep mode. Delete mode, deletes the mail from the mailbox after its retrieval and this mode is used when the user is working at his permanent computer. As the mails can be saved and organized on the user’s permanent computer, it need not be remaining in the mailbox.

Keep mode is used when the user is not working on its permanent computer. In keep, mode mails remain in the mailbox even after its retrieval for later organizing of mails on the user’s permanent computer.

Conclusion

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. It also let user organize the mails.