What is the default port number for the POP protocol?

The correct answer reflects the default port numbers used by the Post Office Protocol (POP) for retrieving emails. POP has two widely recognized versions: POP2 and POP3. POP2, which is an older version, traditionally operates on port 109, while POP3, the more commonly used version today, operates on port 110.

This makes option C accurate, as it includes both of these default ports associated with the POP protocol. Understanding these port numbers is crucial for configuring email clients and troubleshooting any issues related to email retrieval using these protocols.

When considering the other options, it's clear that they do not conform to the standard ports used for POP. For instance, port 143 is designated for the Internet Message Access Protocol (IMAP), while port 220 is typically not associated with either POP protocol. Port 80 is reserved for Hypertext Transfer Protocol (HTTP), which is unrelated to email retrieval. Thus, the ports referenced in option C are significant in the context of email communication.