With roughly a billion active user accounts worldwide, Gmail and Yahoo! Mail are two of the largest email service providers on the Internet today. Outlook (previously called Hotmail), AOL, Zoho Mail, Mail.com, and Comcast individually handle hundreds of millions of user accounts around the globe.Each one of these services (and even the lesser-known ones such as Inbox.com, Hushmail, and GMX) strive to provide the best experience for their users. As a result, each offers an advanced spam filtering system to prevent unwelcome and unwanted emails from reaching the user’s inbox.From the view of the user, these systems are essential and