I have gone to system preferences and removed the checkbox near the mail app for login items. This is fine. But the mail app still starts on boot. If I look at the item in the dock, there is a tick next to the option "open at login". I can not remove this tick! If I select the item and re open the context menu, it's still there. If I do this with any other app, the tick toggles. Mail however, refuses to be unticked and wants to be started with the system. Any ideas?