POP3

POP3 (Post Office Protocol version 3) is a standard internet protocol used by local email clients to retrieve messages from a remote mail server. Its architecture is built around the store-and-forward model, where the server acts as a temporary holding area until the client downloads the data to a local machine.

Operational Workflow

The protocol operates over TCP, utilizing port 110 for standard communication and port 995 for encrypted SSL/TLS sessions. A typical session progresses through three distinct states:

• Authorization: The client authenticates using USER and PASS commands.
• Transaction: The client retrieves message statistics via STAT, lists headers with LIST, and fetches full message bodies using RETR.
• Update: The server commits changes and permanently removes messages marked with DELE after the client issues the QUIT command.

POP3 is primarily used when users need full offline access to their archives or when server-side storage is strictly limited. Unlike IMAP, it does not synchronize folders or message flags (such as 'read' or 'replied') across multiple devices. This makes it less suitable for modern workflows where users access the same mailbox from smartphones, tablets, and PCs simultaneously. A key technical fact: POP3 only downloads the Inbox folder; other server-side folders are inaccessible via this protocol.