Design: Better UX for receiving single messages
The current UX (double click contact to see a window with the one message) is fine if you do not get many single messages / alerts. When you get many from one contact, though, you need to keep double-clicking on the contact until you have seen them all. There is no way to see how many there are or to deal with them all in bulk.
Perhaps a window that lists the subjects/timestamps as a jumping-off point to the messages? Or integrate some viewed/not yet viewed status into the history window and jump there?