What is the primary protocol used for sending email?

The primary protocol used for sending email is Simple Mail Transfer Protocol (SMTP). SMTP is designed specifically for the transmission of email messages between servers and also allows email clients to send messages to the mail server. It operates over the TCP/IP protocol suite and typically uses port 25, although other ports like 587 and 465 are also common for secure transmission of emails.

This protocol handles the process of directing and delivering emails to their final destination. When you send an email, it travels from your email client through your mail server, using SMTP to communicate with the recipient's mail server. Once the email reaches the recipient's server, other protocols such as IMAP or POP3 can then be used to retrieve the received email.

The other options mentioned are primarily for retrieving and managing email rather than sending it. IMAP allows users to access and manage their emails on the server without downloading them, while POP3 downloads emails to a local device and typically deletes them from the server after retrieval. FTP is a file transfer protocol and does not deal with email at all. Therefore, SMTP is indeed the correct answer for the primary protocol used for sending email.