Since upgrading to Mavericks I get a sound whenever I get mail. I find this very annoying so first port of call is to disable ‘Play user interface sound effects’ from System Preferences -> Sound.

This did not work, I found a separate option in mail for playing a sound on incoming mail, disabled that and other actions if you want.

NB: On checking things to write this I found that ‘Play user interface sound effects’ had been enabled again.