The protocol used for sending and receiving email over the internet is known as SMTP, which stands for Simple Mail Transfer Protocol. This protocol is responsible for transmitting email messages from the sender's email server to the recipient's server. For the retrieval of emails, protocols such as IMAP (Internet Message Access Protocol) or POP3 (Post Office Protocol) are commonly used. Together, these protocols form the backbone of email communication, ensuring efficient and reliable delivery of messages across the internet.