No alert sounds for emails??

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.

Except for this, the phone does everything it should do.


TIA for any help in fixing this.