What is POP / POP3 (Post Office Protocol 3)?

POP and POP3 (Post Office Protocol 3) is used to receive mail from a remote server and is the 3rd version of the e-mail protocol.

What is POP and POP3 (Post Office Protocol 3)?

What is the POP3 Mail Protocol?

POP3 allows e-mails to be retrieved from an e-mail server. When you download an e-mail with this protocol, the e-mails are stored locally as the e-mail is deleted from the server.

However, POP and IMAP are only used for server-to-user communication within the ISP’s private network.

Since the server receives mail from another server over the Internet, it uses SMTP as the protocol between both servers.

Unlike other pre-built protocols such as SMTP, POP does not require a permanent connection to the Internet, as it requires the user to send messages stored on the server during the connection.

Another protocol commonly used as an alternative to POP is the IMAP protocol, where it is possible to open mail directly from the server as if it had been downloaded to a computer. In addition, IMAP allows you to delete received messages locally by keeping them on the server.

If you access your account from multiple locations using this protocol, you will not be able to see the emails you have previously received. The messages you download are stored on only one device.

It is not recommended for small businesses due to the high storage requirements of POP3. The POP3 is often a useful protocol for ISPs.

The SMTP protocol is used when the user sends a new e-mail. Also, the connection between e-mail servers is controlled by SMTP. When a user wants to read the newly received e-mail, they will be able to read the e-mail via POP or IMAP. Consequently, it is an email receiving protocol.

This protocol uses TCP port 110 by default. TCP 995 port can also be used for e-mail security and is also defined in RFC 1939.

How the Post Office Protocol Works?

On a computer that is permanently connected to the Internet, mail client programs can be configured to automatically check message requests to the mail server.

As a result, the SMTP is used to send mail, and the POP is used to receive mail.

Most POP mail clients are automatically configured to delete the message from the mail server after successful transmission, but this setting can be changed optionally.

To better understand how the mail protocol works, you can test the Windows Mail application or a 3rd party software by configuring it with this mail protocol.

How POP3 works briefly: The received emails are deleted from the server and stored on the logged-in device. As a result, when you access your account elsewhere, you won’t be able to see the emails you have previously received.


POP works fully compliant with major Internet messaging standards such as Multipurpose Internet Mail Extensions, which allow mail attachments, and works best for users who have a program installed to read mail.

Also, this protocol is useful for users who do not have a permanent connection to the Internet or a network that includes the mail server.

On networks with slow Internet connections, it runs a little slower as it requires client programs to download the full content of each message after authentication.


The latest version of the POP is POP3 and there are several uncommon versions.


MDS is an authenticated protocol and the mail client sends a hash and then ensures that the password is encrypted to the server instead of sending an encrypted password.


RPOP uses a password-like user ID to authenticate requests. However, this user ID is not encrypted, so RPOP is not any more secure than the POP standard.

How to Install It?

A POP server receives mail for authorized users and allows them to download it over the network. A server with these features has three basic components:

   Mailbox Storage

The mailbox storage area is where the server incoming messages are stored on the disk.

   Mailbox Service

The mailbox service enables users to download mail over the network.

   Account Management

With the account management, passwords are determined for authorized users.

How to Make a Server Connection?

To establish a connection to a POP server, the mail client opens a TCP connection on port 110 of the server.

When the connection is established, the server sends an invitation to the client, and then commands and responses defined in the protocol between the server and the client are sent to each other.

In this data communication, authentication is requested from the client where the username and password of the user are sent to the server.

When authentication is successful, the client enters the Transaction State, and the LIST, RETR, and DELE commands are used to view, download, and delete messages from the server, respectively.

Messages defined for deletion are not removed from the server until the client sends the QUIT command to end the session.

At this point, the server enters the Update State, a stage where flagged messages are deleted and all remaining resources of the session are cleared.

   Final Word

In this article, we briefly talked about what is a post office protocol. IMAP is an Email sending service and POP is an Email receiving service. It is recommended to use the IMAP protocol instead, as the storage capacity of the computer that will use this protocol will be seriously full. Thanks for following us!

   Related Articles

What is FTP, What Does It Do?
What is NAT, What Does It Do?
What is TFTP, What Does It Do?
What is Sysprep?
What is Ping?

Add a Comment

Your email address will not be published. Required fields are marked *