The 10.6.5 again breaks Mail plugins. Here is how to fix DockStar and WideMail:
If you have already had your DockStar and WideMail plugins disabled by opening Mail.app you’ll need to look in ~/Library/Mail (or /Library/Mail if you installed globally) and move the files back to the active bundles directory. They’ll typically be in Bundles (Disabled), so quit Mail, find them, and move them back into the Bundles directory.
Fix DockStar
Open Terminal and type this (use ~/Library… if installed globally):
defaults write ~/Library/Mail/Bundles/DockStar.mailbundle/Contents/Info SupportedPluginCompatibilityUUIDs -array-add "857A142A-AB81-4D99-BECC-D1B55A86D94E"
defaults write ~/Library/Mail/Bundles/DockStar.mailbundle/Contents/Info SupportedPluginCompatibilityUUIDs -array-add "BDD81F4D-6881-4A8D-94A7-E67410089EEB"
Fix WideMail:
defaults write ~/Library/Mail/Bundles/WideMail.mailbundle/Contents/Info SupportedPluginCompatibilityUUIDs -array-add "857A142A-AB81-4D99-BECC-D1B55A86D94E"
defaults write ~/Library/Mail/Bundles/WideMail.mailbundle/Contents/Info SupportedPluginCompatibilityUUIDs -array-add "BDD81F4D-6881-4A8D-94A7-E67410089EEB"
Enjoy.