It looks like the spam filter has now kicked in and I have sent two emails both of which were delivered.
The first one with Test as the subject and no text had [-SPAM-] Test as the subject on the received email.
The second one had a 'normal' subject and some text and had [-SPAM-] Matches as the subject on the received email.
I sent both emails again to a Google mail box and a Yahoo mail box. They were not seen as spam.
Do you think I should contact my hosting service and see if they have any ideas ?
(Thanks Townman for the Uceprotectl3 info)