What is Post Office Protocol (POP)?

What is Post Office Protocol (POP)?

The Post Office Protocol (POP) is a standard internet protocol used for retrieving emails from a remote mail server to a local email client.


3 min read

Ever wondered how your email client retrieves messages from a server, especially when you're offline? The answer lies in a crucial protocol called the Post Office Protocol (POP).

What is POP?

The Post Office Protocol (POP) is a standard internet protocol used for retrieving emails from a remote mail server to a local email client. POP3 is the most commonly used version of POP. It is one of the most widely used email retrieval protocols along with IMAP (Internet Message Access Protocol). POP allows users to download emails from their email server onto their local computer or device for offline access.

  • POP3 (version 3) is the most widely used version.

  • POP operates on the Application Layer (Layer 7) of the OSI model.

  • It typically uses TCP (Transmission Control Protocol) for reliable data transfer.

  • Unencrypted, plaintext authentication uses TCP/UDP port 110 and encrypted emails use Secure Sockets Layer/Transport Layer Security (SSL/TLS) over TCP/UDP port 995.

Features of POP

  • Downloads emails: POP retrieves emails from the server to your device.

  • Offline access: Once downloaded, you can access these emails even without an internet connection.

  • Deletion options: POP allows you to choose whether to keep emails on the server after downloading them.

Limitations of POP

  1. Limited Synchronization: POP only retrieves emails. It doesn't keep copies of emails on the server by default. This means you cannot access the same email from multiple devices unless you configure the server to keep a copy.

  2. No Folder Structure: POP does not support server-side folders or labels, meaning that emails are typically organized only within the email client and not reflected on the server.

  3. Security Concerns: POP transmits user credentials and email content in plain text by default, making it susceptible to interception and eavesdropping. However, POP3S (POP3 over SSL/TLS) can address this security concern by encrypting the communication between the client and the server.

Designed for the Past

POP3's design originated in a time when internet connectivity wasn't always reliable. It catered to users with dial-up connections, enabling them to download emails when online and manage them offline.


POP3 played a crucial role in the early days of email, enabling offline access and management. However, for a more comprehensive and secure email experience, IMAP is the preferred choice today. Understanding POP3's functionalities and limitations helps you choose the right protocol for your email needs.

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