Which of the following protocols is primarily used for sending emails?

The correct choice is Simple Mail Transfer Protocol (SMTP), which is the primary protocol used for sending emails over the internet. SMTP is designed specifically for transmitting messages from a sender's email client to the recipient's email server, facilitating the process of sending and routing emails effectively.

SMTP operates on a client-server model, where the email client communicates with the email server to relay the message. This protocol defines how messages are formatted and transmitted, ensuring that emails are delivered accurately and securely.

In contrast, HTTP (Hypertext Transfer Protocol) is mainly used for transferring web pages and other resources on the internet, while FTP (File Transfer Protocol) is utilized for transferring files between computers. IMAP (Internet Message Access Protocol), on the other hand, is used for retrieving and managing emails from a mail server rather than sending them. Each of these protocols serves a distinct purpose that does not include the function of sending emails, making SMTP the unequivocal choice for this specific task.