How can David block POP3 at the firewall?

David is a security administrator working in Boston. David has been asked by the office’s manager
to block all POP3 traffic at the firewall because he believes employees are spending too much
time reading personal email. How can David block POP3 at the firewall?

A.
David can block port 125 at the firewall.

B.
David can block all EHLO requests that originate from inside the office.

C.
David can stop POP3 traffic by blocking all HELO requests that originate from inside the office.

D.
David can block port 110 to block all POP3 traffic.