Sendmail is a widely used mail transfer agent (MTA) that facilitates the sending and receiving of email messages over the Internet. It was developed in the early 1980s and has since become a standard for email routing. Sendmail operates on various operating systems, including Unix and Linux, and is known for its flexibility and configurability. Despite its popularity, Sendmail can be complex to configure, which has led to the development of alternative MTAs like Postfix and Exim. These alternatives often offer simpler setups while still providing robust email handling capabilities. Overall, Sendmail remains an important part of email infrastructure.