The SMTP Protocol (Simple Mail Transfer Protocol) is a standard communication protocol used for sending and receiving email over the Internet. It enables email servers to transmit messages between each other and ensures that emails are delivered to the correct destination. SMTP operates on a client-server model, where the email client sends messages to the server, which then forwards them to the recipient's server. SMTP works primarily on port 25 and uses a set of commands to facilitate the transfer of emails. It is essential for the functioning of email services, allowing users to send messages to others using various email clients like Outlook or Gmail.