Apple Mail under OS X Leopard doesn’t support the GrowlMail Mailbundle which comes as an extra when installing the Growl notificaiton framework. Since I really missed that feature, that has been with me as long as I own a Mac, I searched around the WWW to find a solution.
Luckily there is a way:

  • Quit Apple Mail
  • Download the Growl .dmg from its website and install GrowlMail
  • Launch the Terminal
  • Enter the following two commands
    defaults write com.apple.mail EnableBundles -bool YES
    defaults write com.apple.mail BundleCompatibilityVersion -int 3
  • Start Apple Mail and enable the GrowlMail plugin
  • Be happy ever after :)

via: blimps are cool