I’m a big fan of creating clean and simple applications which can be easily expanded through the use of extensions, hence my love of Firefox. Yet, Firefox isn’t the only application which has extensions, and Apple’s Mail.app, an OS X e-mail client, also has tons of great extensions which expand the functionality of Mail.app and lets it do some pretty cool things. Hawk Wings has an extensive list of plugins and addons for Mail.app which is really cool. Some connect to existing e-mail services like GMail+Growl and the GMail Notifier, while others allow for mail forwarding, provide spoken notification of new e-mail, encrypt e-mail and help Mail.app integrate better into other applications. If you’re a fan of Mail.app and use it often, you will definitely find some cool and useful tools here.