POP3 uses which port number?

POP3 uses which port number?

• A. 110
• B. 119
• C. 123
• D. 563

Answer: (A)

Standard port numbers identify specific services in TCP/IP networks. POP3 is the protocol used to retrieve email from a mail server, and its default port is 110. This is the well-known port assigned for POP3, so clients connect to a server on port 110 to issue POP3 commands and receive responses (without TLS by default; a secure variant uses a different port). The other ports correspond to different services: 119 is NNTP (Usenet), 123 is NTP (time synchronization), and 563 is NNTP over TLS (NNTPS). So 110 is the appropriate port for POP3.

Standard port numbers identify specific services in TCP/IP networks. POP3 is the protocol used to retrieve email from a mail server, and its default port is 110. This is the well-known port assigned for POP3, so clients connect to a server on port 110 to issue POP3 commands and receive responses (without TLS by default; a secure variant uses a different port). The other ports correspond to different services: 119 is NNTP (Usenet), 123 is NTP (time synchronization), and 563 is NNTP over TLS (NNTPS). So 110 is the appropriate port for POP3.