SMTP, or Simple Mail Transfer Protocol, is a set of guidelines for transferring electronic mail between computers. It allows users to send and receive emails via a software program, typically known as a Mail Transfer Agent, or MTA. SMTP servers are responsible for handling all aspects of email delivery, including managing user accounts, handling incoming and outgoing messages, and ensuring that emails are delivered in a timely manner. In addition to providing an essential service for email users, SMTP servers can also be used to send transactional emails, such as order confirmation emails, shipping updates, and notifications. There are two types of SMTP protocols: the end-to-end method and the store and forward method. The end-to-end method is typically used between organizations, while the store and forward method is used within an organization. SMTP rely on two key components: a User Agent (UA) and a Mail Transfer Agent (MTA). UAs are responsible for creating and sending messages, while MTAs are responsible for routing messages to their destination. By working together, SMTP servers provide a reliable and efficient way to send and receive email.