What is the primary function of the SMTP protocol?

The primary function of the SMTP (Simple Mail Transfer Protocol) protocol is to transfer emails between servers. SMTP is specifically designed for sending and relaying email messages, making it crucial for the communication of emails over the internet. When a user sends an email, the client communicates with the server using SMTP, which handles the setup of the email and routes it to the recipient's server.

This protocol is reliable and efficient for transmitting text-based messages and supports attachment features, although it is fundamentally about the delivery of emails rather than managing them after they have been sent, which is where other protocols like IMAP or POP3 come into play.

Other options, such as filtering spam, archiving emails securely, and providing real-time notifications, relate to additional functionalities provided by other systems or protocols but are not the primary responsibilities of SMTP itself. While SMTP handles the delivery of emails, spam filtering, secure archiving, and notifications typically involve separate mechanisms or protocols that work in conjunction with SMTP, rather than being core functions of SMTP.