The purpose of a spam filter in email systems is to identify and separate unwanted or harmful email messages—commonly known as spam. These filters analyze incoming emails based on various criteria, including the sender's address, subject line, and content. By employing algorithms and machine learning, such filters can improve accuracy over time, reducing the chances of legitimate emails being marked as spam (false positives) while catching most spam (false negatives). This helps maintain a more organized and secure email experience for users.