514.3 SMTP, POP3, and IMAP

Understand how email is sent and received using internet protocols that support secure, structured communication.

Overview

In this topic, we explore how email is transferred between systems using dedicated communication protocols. SMTP is used to send messages, while POP3 and IMAP are used to retrieve and manage inboxes. These protocols are fundamental to email applications and illustrate how the Internet supports asynchronous communication through structured standards.

Targets

In this topic, students learn to:

• Explain the function of SMTP in sending email

• Describe how POP3 and IMAP retrieve messages from a server

• Compare POP3 and IMAP based on user experience and technical behaviour

• Understand how these protocols integrate with email clients and servers

• Recognise how protocol design supports accessibility across devices

Syllabus references

Programming for the web

Data transmission using the web

• Investigate and describe the function of web protocols

  • SMTP, POP3, IMAP

Email transmission protocols

SMTP – Sending email

Simple Mail Transfer Protocol (SMTP) is used to send messages from an email client to a mail server, or from one mail server to another.

• Used when clicking “Send” in an email application

• Pushes the email to the recipient’s mail server

• Only supports outbound messages

POP3 – Download and delete

Post Office Protocol version 3 (POP3) retrieves emails by downloading them to a local device, then typically deleting them from the server.

• Simple and resource-efficient

• Works best on a single device

• Not suitable for users who check email from multiple devices

IMAP – Server-based access

Internet Message Access Protocol (IMAP) allows users to view and manage emails while keeping them stored on the server.

• Supports synchronisation across devices

• Reflects folder structure and message status across platforms

• Common in cloud-based email systems

SMTP sends email to the server. POP3 downloads and deletes messages. IMAP keeps emails on the server for access from multiple devices.

Summary

SMTP, POP3, and IMAP are the core protocols that allow emails to be sent and received over the internet. Each serves a different purpose: SMTP for sending, POP3 for downloading, and IMAP for synchronised inbox access. Understanding these protocols helps clarify how everyday communication is handled behind the scenes.