The standard TCP port for unencrypted POP3 email retrieval is 110.
POP3, or Post Office Protocol version 3, was designed for downloading messages from a mail server to an email client. Its original operating model suited dial-up users: a client connected, retrieved mail, and could delete the downloaded messages from the server for later offline reading.
Port 110 is the well-known port assigned to ordinary POP3 connections. The session is unencrypted unless the client and server negotiate encryption with the STLS command. This is different from SMTP submission ports, such as 587, which are used to send outgoing mail, and from IMAP port 143, which is another protocol for accessing incoming mail.
A common source of confusion is that “unencrypted” describes the connection’s transport security, not necessarily the password method or message contents. POP3 can support authentication extensions, but a connection on port 110 should not be assumed secure. POP3 over implicit TLS conventionally uses port 995 instead. POP3 also differs from IMAP because it traditionally emphasizes downloading messages rather than maintaining a synchronized mailbox across multiple devices.