POP3, or Post Office Protocol version 3, is a standard protocol used by email clients to retrieve emails from a server. It allows users to download their emails to their local devices, making it easier to read and manage messages offline. Once downloaded, emails are typically deleted from the server, although some configurations allow for messages to remain on the server. POP3 is widely supported by various email services and clients, making it a popular choice for users who prefer to access their emails without needing a constant internet connection. However, it is less suitable for users who want to access their emails from multiple devices, as it does not synchronize messages across them.