The Simple Mail Transfer Protocol (SMTP) is used for sending emails over the internet. This communication protocol facilitates the transfer of email messages between servers, ensuring that messages are transmitted efficiently and accurately. SMTP works by sending the email data to the recipient's email server, which then stores and forwards the messages to the recipient's inbox. Additionally, SMTP can interact with other protocols like IMAP or POP3 for retrieving messages, making it a fundamental component of the email delivery process.