What protocol is primarily used to send email?

The protocol primarily used to send email is Simple Mail Transfer Protocol (SMTP). This protocol is specifically designed for sending emails across the Internet. It facilitates the transfer of messages from the sender's mail server to the recipient's mail server, ensuring that emails reach their destination efficiently and reliably.

SMTP operates over the TCP/IP protocol suite, typically using port 25 for communication. It is responsible for routing the messages and handling errors during transmission, making it a crucial element in the email infrastructure.

In contrast, other protocols mentioned serve different purposes in the realm of email. For instance, HTTP (Hypertext Transfer Protocol) is primarily used for transmitting web pages on the Internet. FTP (File Transfer Protocol) is used for transferring files between computers and is not specifically related to email transmission. POP3 (Post Office Protocol version 3) is used for retrieving emails from a mail server after they have been sent, focusing on the process of receiving rather than sending. Understanding these distinctions clarifies why SMTP is the protocol designated for sending email.