This makes SpamSieve play a sound when new good messages are received (as described in the Settings ‣ Notification section). To add a sound to the menu, copy the sound file to the Sounds folder in your Library folder. (See the How can I open the Library folder? section.) SpamSieve will also look for sounds that are built into your installed e-mail programs.
You can adjust the Alert volume in the Sound Effects tab of the Sound pane in System Settings. If the volume is set to zero, the Mac flashes the screen instead of playing the sound.
If you are not hearing the sounds, make sure that you have selected an appropriate speaker in the Play sound effects through pop-up menu.