Remove the Mail plugin System-wide
- Quit Mail
- Open Finder, press Command+Shift+G, go to the following path:
/Library/Mail/Bundles/
- Select the plugin to remove, right-click and Move to Trash
- You can now open Mail and the plugin will be removed
Remove the Mail plugin for a single User
- Quit Mail
- Open Finder, press Command+Shift+G, go to the following path:
~/Library/Mail/Bundles/
- Select the plugin to remove, right-click and Move to Trash
- You can now open Mail and the plugin will be removed
Credits:
http://osxdaily.com/2014/02/05/uninstall-mail-app-plugin-mac-os-x/