I have configured Mail.app to make a sound (a short MP3 file) when new mail arrives. This used to work a few years ago. For the past few years it hasn't worked. User interface sounds are switched on and everything is activated in System Preferences and Mail preferences. When I check the settings for the MP3 file in Mail preferences, it even plays the file there. But when a new mail arrives it does not. Simiarly, and I don't know if this problem is related or not, Skype has stopped making user interface sounds. Again, this is the same Mac, which is configured for user interface sounds in System Preferences, and Skype is configured to make a ringing sound when I call someone and some weird sound when I receive an instant message in a chat window. Any ideas?