Fixing GrowlMail for Mail 4.2
Lately Apple has been revving the version number (and plugin compatibility UUID) of Mail.app with every version of 10.6. This breaks bundles like GrowlMail even when they are still compatible. The easy fix (although not necessarily the best if it turns out an update is required!) is to run a few commands in Terminal to add the new UUIDs1 to the SupportedPluginCompatibilityUUID key in the Info.plist.