The email protocol first defined in RFC 1081 was POP3, the Post Office Protocol version 3.
Published in November 1988 and authored by M. T. Rose, RFC 1081 described a simple way for workstation clients to access messages stored on a mailbox server. POP3 was designed around straightforward retrieval: a client connects, authenticates, lists or downloads messages, and can mark them for deletion. Its simplicity helped it work well on early, intermittently connected networks.
RFC 1081 was later obsoleted by RFC 1225, and the better-known modern specification is RFC 1939. POP3 generally downloads mail to a client, although later extensions and client settings can leave copies on the server. It is therefore different from IMAP, which is designed for synchronized access to mailboxes and folders across multiple devices.
SMTP is another frequent mix-up, but it handles sending and relaying mail rather than retrieving it from a mailbox. HTTP transfers web resources, not ordinary mailbox messages. POP3 commonly uses TCP port 110 without encryption and port 995 when wrapped in implicit TLS, though secure deployment details depend on the service.