For Growl 1.3 (App Store) to work with Mail.app under 10.7.1, you need to install the actual GrowlMail 1.3
Update: GrowlMail1.3 does not work with Mail.app 5.1 (OS X 10.7.2), there’s a new version 1.3.1 that does work.
Growl 1.3 and Mail.app
1
For Growl 1.3 (App Store) to work with Mail.app under 10.7.1, you need to install the actual GrowlMail 1.3
Update: GrowlMail1.3 does not work with Mail.app 5.1 (OS X 10.7.2), there’s a new version 1.3.1 that does work.