Which protocol is primarily used for sending email?

The protocol primarily used for sending email is SMTP, which stands for Simple Mail Transfer Protocol. SMTP is specifically designed for the transmission of email messages from a sender's device to the email server and between servers. It operates on the principle of sending messages in a straightforward manner, ensuring efficient delivery.

SMTP establishes a set of rules for how email should be formatted and transmitted between servers, making it a critical component of the email infrastructure. This ensures that email can be reliably sent across the Internet to the intended recipient. While there are other protocols in use for handling emails, such as IMAP and POP3, these primarily focus on retrieving email from a server rather than sending it.

FTP is primarily used for transferring files between systems, and HTTP is used for fetching web pages and resources from the web. Neither of these protocols is designed for email transmission. Consequently, SMTP stands out as the correct choice due to its dedicated purpose and functionality in the realm of email communication.