Which of the following protocols is NOT used for sending electronic mail?

The correct answer is identified as the protocol that is not used for sending electronic mail. FTP, or File Transfer Protocol, is primarily designed for transferring files over a network and does not facilitate email transmission.

In contrast, the other protocols mentioned play significant roles in the email ecosystem. SMTP, or Simple Mail Transfer Protocol, is the standard protocol for sending emails across the Internet. IMAP, or Internet Message Access Protocol, and POP3, or Post Office Protocol version 3, are both used for retrieving emails from a server. IMAP allows users to access and manage their email on the server, while POP3 downloads emails for local storage. Understanding the specific functions of each protocol clarifies the role they play in email communication and helps delineate the function of FTP as unrelated to email transmission.