I’m going to port some more of my technical articles from tumblr over here. This is an oldie but goodie as I still get a lot of traffic for it. Original post is here.

Sometimes when new versions of Mail.app come out, the plugin architecture isn’t always backwards compatible. To disable plugins that could potentially crash Mail.app, a plugin verification occurs via a PluginCompatibilityUUID check.

So, you need to (WideMail is used in this example):

• add the Message.framework PluginCompatibilityUUID to the SupportedPluginCompatibilityUUIDs of each plugin
• add the Mail.app PluginCompatibilityUUID to the SupportedPluginCompatibilityUUIDs of each plugin

Add the Message.framework PluginCompatibilityUUID

1. Open up /System/Library/Frameworks/Message.framework/Resources/Info.plist and search for PluginCompatibilityUUID. In 10.6.5, this is 857A142A-AB81-4D99-BECC-D1B55A86D94E.
2. Open up ~/Library/Mail/Bundles/WideMail.mailbundle/Contents/Info.plist and search for SupportedPluginCompatibilityUUIDs. Add a new string to this array with the value 857A142A-AB81-4D99-BECC-D1B55A86D94E.

Add the Mail.app PluginCompatibilityUUID

1. Open up /Applications/Mail.app/Contents/Info.plist and search for PluginCompatibilityUUID. In Mail.app 4.4, this is BDD81F4D-6881-4A8D-94A7-E67410089EEB.
2. Open up ~/Library/Mail/Bundles/WideMail.mailbundle/Contents/Info.plist and search for SupportedPluginCompatibilityUUIDs. Add a new string to this array with the value B842F7D0-4D81-4DDF-A672-129CA5B32D57.

Done.

This is a kluge and there is a reason Apple requires this check. It’s best to wait until the official developer releases an updated plugin.