POP3 Post Office Protocol
Mail retrieval protocol. RFC 1939 (1996, v3 still the only relevant one). Default pattern: download mail to client, delete from server. Outdated compared to IMAP.
Port 110 (unencrypted) or 995 (POP3S). Distinct from IMAP: POP3 is "fetch and delete", IMAP is "sync state with server". POP3 useful for: single client, limited server storage, offline reading. Modern use: almost none — all webmail + smartphone mail clients use IMAP or Exchange/JMAP. POP3 lives on in some hosting providers + nostalgic configurations.