I’m having a strange problem with Apple Mail. Sometimes when new email messages arrive, I get the new mail sound. But other times when new email messages arrive, Mail doesn’t make any sounds at all. Any ideas as to what’s going on here?

First, double-check that your Mail preferences are set to play a sound when new mail arrives (go to Mail > Preferences > General and look for “New messages sound”). Next, go into System Preferences > Sound and verify that the checkbox is checked for “Play user interface sound effects.”

If both of those are set correctly, then you’re likely experiencing a bug in Mail related to the IMAP IDLE command. If you’re checking your email from an IMAP server that supports the IDLE command, your emails are actually being pushed to Apple Mail in real time as soon as those messages arrive. But Apple Mail’s new-mail sound doesn’t work with push email; it only works with emails that Mail pulls from the server itself. It pulls messages when you click the Get Mail button or when it automatically checks for new mail based on its schedule in Preferences.

You can configure GrowlMail to show a floating notification window for new mail, as well as play an optional sound.

To get your sounds back, you could disable your push email altogether by going into each email account and unchecking the option to “use IDLE command” (Mail > Preferences > Accounts > Advanced). Or you can turn off the new-mail sound in Mail’s preferences and hand off this responsibility to GrowlMail (free, growl.info). GrowlMail will pop up a visual indicator and an optional sound whenever new messages arrive in Mail, whether they were pushed or pulled.

If you want Growl to use the exact same new-mail sound that Mail does, you’ll need to make a copy of the New Mail.aiff file from Apple Mail (right-click Apple Mail in the Finder, choose Show Package Contents, and then open the Resources folder), and place it into your ~/Library/Sounds folder.