Many thanks, FloBear. Yes (as I said) I thought I had it sussed, but that 'Forum settings' change just changes the 'replies notification' default settings' to off i.e. the reply box appears with 'email me when a response is made' box un-ticked.
I have to say, I'm not getting anything like as many notifications as I was, but I can't quite understand how those that do are getting through.
Btw, I'm with IE Windows 7.