If anyone can help me isolate the cause of this issue, I'd greatly appreciate it!
OK, I tried activating the sound on T/bird.
First thing to note is that it had Custom enabled, so I tried using the Default sound system ...... which did not work.
I went back to selecting a sound to be played ...... the one there by default would not work -- I suspect it did not exist.
So I navigated to
and selected the first wav file I came across.
Clicking Play after selecting it, played the file.
On further investigation, there are lots of files that will not play ...... so I suppose some specific format is required.
I now have my email sound set to rock.wav
Hope that helps.