An SMTP server, also known as a Simple Mail Transfer Protocol server, is a computer program that is responsible for sending and receiving emails over the internet. It acts as a digital post office, routing emails from one user to another through a series of networks and servers. The SMTP server uses a set of rules and protocols to ensure that emails are delivered to the correct recipient and that they are not intercepted or altered during transmission. It is an essential component of the email system, allowing users to communicate and exchange information quickly and efficiently. Without an SMTP server, emails would not be able to reach their intended destination, making it a crucial element of modern communication.