THANK YOU, this fixed it. My site email address was blank. Im in favor of making that a required field with a default (e.g. noreply@drupal.site), but maybe because that is because I just got burned! :)

Thanks again,
Chris

What happens if you change the Drupal site email address to the same
>From address that one the successful test emails you sent used? Or
change your previously successful test emails to come from your Drupal
site address?

I suspect that your Drupal site address isn't allowed to relay through
your MTA/smarthost.

--
Cheers
Anton