A really great add-on Rated 5 out of 5 stars
This was recommended to me when I posed the problem and it exactly fulfils my requirements in exactly the transparent way I wanted it to work.
You’ve got a Play Sound option added to your filter actions. You get to choose your sound. [I’m using the famous Wallender ringtone - suitably shortened.] No longer do I have to look at my few hundred a day incoming email stream all the time to check if that important or personal email has come in.
An insanely good add-on which sits in the background and it works with T’bird 3.