POP3 is a protocol for downloading email messages from a server to a single device. It was designed for a time when servers were small, connections were slow, and people typically checked mail from only one computer.
POP3 usually removes messages from the server once downloaded, which can lead to fragmentation when multiple devices are used. It provides minimal folder or state management compared to more modern approaches.
POP3 focuses on transferring complete messages rather than synchronizing them. Because of its simplicity, POP3 remains supported almost everywhere, though it is declining in use. It can be configured to keep messages on the server, but this is optional and not part of the original model.
POP3 can be useful for low-storage or offline-first workflows. Its command set is intentionally small so implementations are easy to build.
POP3 is often replaced by IMAP when full multi-device sync is required. POP3 still forms part of the historical backbone of email technology.