Which of these protocols is primarily focused on sending email?

Simple Mail Transfer Protocol (SMTP) is primarily focused on sending email. It is the standard protocol used for transferring email messages between servers and from clients to servers. SMTP is responsible for the process of sending messages from an email client to an email server or between servers until it reaches its destination.

When a user sends an email, their email client communicates with the SMTP server to send the message. SMTP operates on the application layer of the Internet Protocol Suite and works in conjunction with other protocols, such as IMAP or POP3, which are used for retrieving and managing emails once they have been delivered to the recipient's server.

Other protocols mentioned, such as IMAP and POP3, are focused on retrieving and managing emails rather than sending them. IMAP allows users to access and manage their email directly from the server, while POP3 downloads emails to a local device and usually deletes them from the server. Hypertext Transfer Protocol (HTTP) is primarily used for transferring web pages and resources on the internet, and is not related to email transmission.