Is that the complete message? If there is more content, that may help. It may be that the sending IP is blacklisted, as your IP is different from your web host.

Thanks. I read the message more closely after receiving your reply, and I think it was an authentication issue. Seems to be working now.

My son seems to have found a solution. This is part of his email

"The tag has been added onto the DNS" and further "it's a known change google did".

I don't understand but the fix seems to work. Good luck out there.