POP3 (Post Office Protocol version 3, RFC 1939) is a standard protocol for retrieving email from a remote mail server to a local client. It is one of the foundational email access protocols alongside IMAP.
POP3
POP3, the third version of the Post Office Protocol standardized as RFC 1939, is one of the oldest and simplest ways for an email client to pull messages down from a mail server. Its model is deliberately minimal: connect, authenticate, download messages to the local device, and typically delete them from the server. That single-device, download-and-remove design is what distinguishes it from the server-side, multi-device model of IMAP.
- Download-and-delete by default - Messages are pulled to one client and usually removed from the server, keeping the server stateless and storage-light.
- A small command set -
USER,PASS,STAT,RETR,DELE, andQUITcover essentially the whole protocol. - Runs over TCP - Historically on port 110, with the TLS-secured variant (POP3S) on port 995.
- Client-side mailbox - Mail lives on the user’s machine, which fit an era of intermittent, single-computer connectivity.
POP3 is a protocol most teams inherit rather than choose today, since IMAP and web/API-based mail access better fit multi-device use. In the API economy it still surfaces at the edges — legacy integrations, mailbox-polling automations, and email-ingestion services — but modern systems increasingly reach mail through HTTP APIs like Gmail and Microsoft Graph instead. It remains useful as a reference point for how a clean, tightly-scoped protocol spec reads, next to newer email interfaces.
