What is POP3 (Post Office Protocol Version 3)?

Last Updated : 30 Jan, 2025

Today email is the most widely used platform for personal and professional business communication. Email protocol is defined as a set of rules for the secure transmission of emails over the Internet. SMTP, IMAP, POP, and POP3 are some of the email protocols. Each type of protocol used has a specific mechanism. The below article covers in detail the POP3 protocol.

Introduction to POP

POP stands for Post Office Protocol. The POP protocol was published in the year 1984. POP has been updated two times namely "POP2" and "POP3". The POP protocol is an Internet Standard Protocol that works on the application layer. It is used to get an access email from the mail server. The need for POP mainly arises when the user or client does not have a continuous internet connection and wants to receive email messages. The Pop client makes use of POP to pull email messages from the POP server. POP3 is the updated version of POP.

What is POP3?

POP 3 stands for Post Office Protocol Version 3. POP3 protocol is used to provide access to the mail inbox that is stored in the email server. POP3 protocol can download and delete messages. Once the POP3 client has established a connection with the mail server it can easily retrieve all the messages from the server. The user can access the messages locally even if the user is offline. The protocol does not inherently support real-time synchronization or automatic checking for new messages, users can configure their email clients to check for new messages at intervals or manually. Many email programs, including Apple Mail, Gmail, and Microsoft Outlook, support the POP3 protocol, although IMAP is often preferred for its synchronization features.

When a message is sent, SMPT is used to transfer it from the client to the server and ultimately to the server of the recipient. However, the Message Access Agent facilitates the transmission of the message from the receiving server to the host server. POP3 and IMAP are the two types of protocols that are included in the Message Access Agent.

POP3 Ports

POP3 makes use of two network ports. They are:

Port 110: Port 110 is a default TCP port used by POP3. But It has a disadvantage that it does not support encrypted communication.
Port 995: Port 995 is majorly used for more secure applications. Port 995 is a TLS or SSL port used to provide more security.

History of POP3

In 1984, the Internet Engineering Task Force published RFC 918, the initial version of post office protocol. The POP3 protocol was created by the engineers as a straightforward and efficient email protocol that is used to retrieve emails from the server. Instead of accessing the mailbox offline, this offers the option to access the mails offline.

RFC 937 introduced the post office protocol version 2, which was superseded by RFC 1081 in 1988, which introduced the post office protocol version 3. Before POP3 was released, it underwent ten more years of revisions. After it was fully polished, it was released in 1996.

The POP3 protocol was developed with the fundamental idea that when a client and a server retrieve mail, it goes through three stages. This is true even if the protocol has experienced many improvements. They made an effort to keep this protocol as simple as possible, and because of its simplicity, it is now widely used.

Working of POP3

Initially POP3 needs to establish a connection between the POP client and the POP server.
Once a secure connection is established several commands are exchanged between them to perform the task.
Once a connection is established client requests available email messages.
The Server sends the available messages along with their size and unique identifier number.
Once the client receives the message, it makes a request to the server for downloading the messages. The user marks such messages and sends them to the server.
Upon receiving from the client-server sends the messages selected by the client and accordingly marks them as read or unread.
The client if want sends a request for deleting the messages.
Once the tasks are completed the client sends a close connection request to the server
The server then sends an acknowledgment to the client and closes the connection.

Advantages of POP3

The message can be read offline also.
POP3 requires less storage space.
POP3 is easy to use and configure.
POP3 is supported by many email applications.
Since our PC already has the emails stored there, accessing them is quick and simple.
The size of emails we send and receive is unrestricted.
Since all emails are kept locally, less server storage space is needed.

Disadvantages of POP3

POP3 does not provide the feature of real-time synchronization.
If an email consists of virus attachments it can affect the system easily.
POP3 does not support accessing the same email at the same time on different systems.
At a time entire email folder can be discarded.
It is also possible for the email folder that is downloaded from the mail server to get corrupted.
Since the emails are kept locally, anyone using your computer can access the email folder.

Difference Between POP3 and IMAP

POP3	IMAP
POP is a simple protocol that only allows downloading messages from your Inbox to your local computer.	IMAP (Internet Message Access Protocol) is much more advanced and allows the user to see all the folders on the mail server.
The POP server listens on port 110, and the POP with SSL secure (POP3DS) server listens on port 995	The IMAP server listens on port 143, and the IMAP with SSL secure (IMAPDS) server listens on port 993.
In POP3 the mail can only be accessed from a single device at a time.	Messages can be accessed across multiple devices.
To read the mail it has to be downloaded on the local system.	The mail content can be read partially before downloading
The user can not create, delete or rename email on the mail server.	The user can create, delete or rename an email on the mail server.