You can block unwanted email according to email address, subject, any header, recipient, or even phrases inside the body of the message.
Just use the drop down menus to choose what you want blocked. For example, you might want to filter out porn sites. You could choose Subject, Body or Any Header from the first drop down menu, and Contains from the second drop down menu. Then type a phrase or word that frequently appears in the header or body of email you receive that promotes porn sites.
To block email from a specific source, just choose From in the first drop down menu, then Equals from the second menu. Type in the person's email address in the box and click Activate.