What is the POP Protocol in Computer Network?

POP (Post Office Protocol) is a standard email retrieval protocol that allows email clients to download messages from a remote mail server. It provides a mechanism for users who don't maintain permanent internet connections to receive their emails by pulling them from a centralized server.

Consider a scenario where user A connects to the Internet using a dial-up connection. When user B sends an email to A while A is offline, the message gets stored in A's mailbox on the ISP's mail server. When A connects later and opens their email client, the client's POP component contacts the ISP's POP server, which then retrieves and downloads the stored emails to A's local machine.

How POP Works

The POP protocol operates through a simple client-server model where the email client acts as the POP client and communicates with the POP server hosted by the email service provider.

Why POP is Required

Email systems face a fundamental challenge: SMTP servers expect recipient computers to be online continuously to establish TCP connections and deliver messages directly. However, most personal computers are not permanently connected to the internet, especially in dial-up or intermittent connection scenarios.

POP solves this problem by introducing an intermediary mail server that:

• Stores incoming emails − Acts as a temporary repository when the recipient is offline

• Provides on-demand access − Allows users to retrieve emails when they connect

• Enables offline reading − Downloads emails to local storage for later access

POP vs IMAP

Conclusion

POP protocol enables email retrieval for users without permanent internet connections by storing emails on a central server and allowing clients to download them on-demand. While newer protocols like IMAP offer more features, POP remains useful for simple, single-device email access scenarios.