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What is Post office protocol 3 (POP3)?

April 21, 2018
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Electronic mail is the core of modern communications. People rely on email to conduct their business and stay in touch with families. The ubiquity of an email availability is one of the strengths of the internet whose phenomenal growth and popularity are also due to the popularity of an email. E-mail system has become the most popular computer based method used to send and receive E-mail messages between the network clients inside or outside the local network. The most important point in E-mail system processes is to send and retrieve the E-mail message in the best delivery time without any delay or latency.

Overview of POP 3?

Post Office Protocol version 3 (POP3) is a standard mail protocol used to receive emails from a remote server to a local email client. This protocol is generally used for receiving email over the Internet. POP3 server must be connected to read email from an email account. After connected with the server, all the email messages in an email account are numbered from 1 and the particular account is locked. This specified number identifies email in the given account. The account number is not changed even if the mail is deleted but the account number can be changed when the connection is closed. Always POP3 account uses only one connection at any one particular time. So that only when the present connection is closed, the new incoming email can be posted in the account.

All the Email delivery models show how email servers as well as email clients are connected with each other. Three different models are used in the internet to deliver email namely; Online, Offline and Disconnected models. In this research, protocol POP3 is designed to work using the offline model. In this offline model, a client node connects online with an email server, downloads the mail, and node goes to offline. Now all mail and its attachments are stored on the client node and completely deleted from the email server. The user can do all the work related with the mail like reads, prints, deletes the mail while the client node is offline. Figure 1 shows the mail transferred from client machine using remote mail server.

PoP3 Diagram

Figure 1: POP 3 Demonstration

POP3, sometimes referred to as just “POP,” is a simple, standardized method of delivering e-mail messages. A POP3 mail server receives e-mails and filters them into the appropriate user folders. When a user connects to the mail server to retrieve his mail, the messages are downloaded from mail server to the user’s hard disk.

Significance of POP 3

POP3 allows you to download email messages on your local computer and read them even when you are offline. Note, that when you use POP3 to connect to your email account, messages are downloaded locally and removed from the email server. This means that if you access your account from multiple locations that may not be the best option for you. On the other hand, if you use POP3, your messages are stored on your local computer, which reduces the space your email account uses on your web server.

By default, the POP3 protocol works on two ports:

  • Port 110– this is the default POP3 non-encrypted port
  • Port 995– this is the port you need to use if you want to connect using POP3 securely

How does Post Office Protocol Work?

When a user checks for new email, the client will connect to the POP3 server. The email client then supplies its username and password to the server for authentication. Once connected, the client issues a series of text-based commands to retrieve all email messages. It then stores these downloaded messages on the user’s local system as new emails, deletes the server copies and disconnects from the server. By default, the server emails are deleted once they are retrieved. As a result, the emails are tied to that particular machine and it would not be possible to access the same emails from an email client on another machine. The user could get around this issue by configuring the email client settings to leave a copy of the emails on the server. POP frees up mailbox space on the server because emails and attachments are downloaded and deleted at server-end whenever the email client checks for new mails. Offline email messages stored in the user’s computer do not have mailbox size limitations except for the hard drive storage capacity of the PC. One drawback of POP3 mail accounts is that it is difficult for the user to export mails if they decide to switch email programs or computer systems.

Advantages of POP3: –

  • Emails are downloaded to the user’s computer. Messages can be read when user is offline.
  • Opening attachments is quick and easy as they are already downloaded.
  • Less server storage space required; all emails are stored on local machine.
  • Storage capacity of emails limited by the size of your hard disk.
  • Very popular, easy to configure and use.

Disadvantages of POP3: –

  • Emails cannot be accessed from other machines (unless configured to do so).
  • Exporting the local mail folder to another email client or physical machine can be difficult.
  • Email folders can become corrupted, potentially losing the entire mailbox at once.
  • Email attachments may contain viruses which may expose the user’s PC to harm if they are opened locally and their virus scanner is unable to detect them.


[1] Hussein Al Bazar, R. Sureswaran and O. Abouabdalla, “A New Approach to Enhance E-mail Performance through POP3 Protocol”, International Conference on Network Applications, Protocols and Services, 21 – 22 November 2008.

[2] “Email Protocols – POP3, SMTP and IMAP Tutorial”, available online at:

[3] “Chapter 4: Congestion Control and Fragmentation in IoT”, available online at: available online at:

[4] Conrad Chung, “Understanding Post Office Protocol (POP3)”, available online at:

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