Sorry Jason, I didn't explain that very well.
When I said test page I just meant a page on the site that I was using to test the form before making it a page people could visit from elsewhere on the site.
So it worked in testing with a couple of my email addresses.
But it doesn't work with the email address it actually needs to use.
But I know that email address does work if I just send an email rather than send a form.
And we have checked junk folders in case they were in there.