POP3 connections are established over which transport protocol?

POP3, or Post Office Protocol version 3, is a standard protocol used for receiving emails. It relies on a reliable transport protocol to ensure that email data is accurately transmitted between the mail server and the email client. The correct transport protocol for POP3 is TCP, which stands for Transmission Control Protocol.

TCP is a connection-oriented protocol that provides a reliable communication channel by establishing a connection between the client and server. It ensures that data packets are delivered in the correct order and without loss, which is crucial for email retrieval. This reliability is essential for email protocols since users need to be confident that all emails are properly fetched and that their content is intact.

UDP, or User Datagram Protocol, is connectionless and does not guarantee delivery or order, making it unsuitable for protocols like POP3, which require reliable data transmission. SCTP (Stream Control Transmission Protocol) is also a connection-oriented protocol but is primarily used for signaling in telecommunications rather than email retrieval. IPX (Internetwork Packet Exchange) is an older network layer protocol that is not used for email retrieval and is largely outdated.

Thus, the establishment of POP3 connections over TCP ensures the necessary reliability and integrity needed for effective email communication.