MOApps Mail Boy

MailBoy periodically searches for new unread messages in your Mail.app Inbox and displays them incl.

preview in an unobtrusive HUD on top of all other Apps - enabling you to decide what to do next.
Ignore them for now.
Answering them.
Deleting them or even mark them as junk mail.

If you like, MailBoy can be used as a Menu bar application with custom Global Hotkey and hidden Dock icon. You can customize its behavior to your needs and the shortcuts from Mail.app are available in MailBoy, too…