Mozilla Thunderbird is an open-source, free and cross-platform mail client and news reader for most modern operating systems including, but not limited to Windows, Macintosh and Linux. It offers some advantages over other mail clients, including junk mail classification. Built from Mozilla code, Mozilla Thunderbird uses Gecko, the most standards-compliant rendering engine in existence. In addition to the feature set found in Mozilla Mail, Thunderbird has several new features and improvements to make your mail and new experience better.