The protocol used for sending emails over the internet is Simple Mail Transfer Protocol (SMTP). SMTP facilitates the transfer of email messages from the sender's mail server to the recipient's server. It uses a push model where the sending server communicates with the receiving server to deliver the messages. SMTP is essential for email communication, allowing users to send messages efficiently and reliably. While SMTP handles outgoing mail, other protocols like IMAP and POP3 are used for retrieving and managing incoming mail.