Hmmmm, after much head scratching and reading "help" articles, I THINK I've solved the issue, sorry it took so long
Well, I found a setting that looked incorrect, so changed it to the "correct" value and 201 emails that were "stuck" in a queue started to get sent out from the forum.
The bad news is that my inbox is now stuffed full of notification emails
Is this working for others? - and apologies if the "wave" of notifications has bunged up your inbox, hopefully things should work more smoothly now........ fingers crossed.