My Curve 8520 has stopped giving me an alert sound for incoming emails despite the alert sound settings being unchanged. I get sound alerts okay for PIN messages & SMS, just not for incoming emails. The email app shows a visual alert (red star on app icon) but there's no sound when they arrive. Email sound alerts definitely used to work properly on this phone.

I've tried a battery-pull with phone switched on, even re-installed the OS but no avail.

TIA for any help in fixing this.