The protocol used to send emails over the Internet is Simplified Mail Transfer Protocol (SMTP). SMTP facilitates the sending and receiving of email messages between clients and servers. When an email is sent, the client communicates with the SMTP server, which processes and routes the message to the recipient's email server. This protocol ensures that emails are properly formatted and directed to the correct destination. SMTP works in conjunction with other protocols like Post Office Protocol (POP3) and Internet Message Access Protocol (IMAP) for retrieving and managing emails from the server.