POP3 (Post Office Protocol version 3) is a protocol used by email clients to retrieve emails from a mail server. It allows users to download emails from the server to their local computer and manage their email locally.
POP3 is one of the oldest and simplest protocols used for email retrieval. It operates over TCP/IP and is designed to support offline mode of email processing. When an email client connects to the POP3 server, it downloads all the emails to the local device and, depending on the settings, may delete the emails from the server. This makes it different from IMAP, which allows for emails to be managed directly on the server.