The settings on my Mac Pro V 10.7.3 were already set per your instructions. The Mail App WAS making outgoing mail sound, but quit - not sure exactly when. Tried a complete shutdown and restart - no change / still no outgoing mail sound. System Alert sound was ok - all seemed ok - switched output source, no help. Switched back to Internal Speaker. I un-checked and re-checked the 'Play sounds for other mail actions' checkbox - still did not seem to work. Closed and then re-opened Mail - again unchecked and re-checked 'Play sounds...' and it all started working as before. Strange. Thanks for help -you got me looking in the right area.
Yes me too. After trying all the tips in bowlerboy's post nothing changed. Although IDLE was selected for iCloud mail (which it now is not). After no success it dawned on me that my Mac also had not been making the start up sound for a while either. Rechecked (toggled off and back on) all settings through System Preferences and rebooted - ALL GOOD! Thanks for all the posts and help *whooosh*