Just in time for the upcoming release of OS X 10.9 Maverick we are releasing the new version of MailPluginFix. With the new version 1.2.0 you will be able to fix your none working mail plugins from Snow Leopard to Mavericks.
As with any major release of OS X please be warned that there is the possibility that the plugins won't work after using this tool! In this case you will have to wait for the plugin developer to release a new plugin version.
For the full list of changes please have a look at the changelog.