OK, have got a little further.
Can now send to external but not receiving anything.
So, if firstname.lastname@example.org
(ISPC) sends to email@example.com
that works fine. If I reply from firstname.lastname@example.org
to that message it disappears. No bounce, no delivery. It's probably the rollernet thing. I'll keep checking.
Also, when I log in the client it does ask for a password which it accepts.