Confused now.
In Thunderbird, using default settings, I get nowhere. No send or receive.
But Changing the incoming Port from the Default 995 to 110 (same as Live Mail) I get a message at the bottom of the screen 'connected to mail.btinternet.com' and the 'green worm' running ion the bottom right corner of the screen as if mail is being collected. And that just goes on and on and on, with no mail arriving!
btw, for a real computer numpty, what do these Port numbers mean?