What is the primary use of the Simple Mail Transfer Protocol (SMTP)?

The primary use of the Simple Mail Transfer Protocol (SMTP) is electronic mail transmission across IP networks. SMTP is a protocol that outlines how email messages are sent from one server to another and specifies how mail clients interact with the mail server to send messages. It operates over the Internet and is an essential part of email communication, enabling the transfer of emails between senders and recipients.

While there are other protocols involved in email communication, such as IMAP and POP3, which are used for retrieving messages, SMTP is specifically designed for the sending aspect of email. This clarity in purpose is what distinguishes SMTP from other options like secure data transmission, file transfer, or database management, which are governed by completely different protocols and mechanisms.