Yay! Ok, its all working now.
I opened a support ticket and it came back with "you do not have dmarc set anywhere". They could also have said "you big dummy"
All of my problems were at the DNS side. I had pasted the DKIM public key wrong, I did not set a dmarc record. Really basic stuff.
Instead of catching this I got tunnel vision and began to study the API for EXIM, reading scripts, looking at low level details.
Richard G. thank you very much for the dialogue. It helped me to snap out of the tunnel and change what I was doing. You were very helpful.
For anyone else hitting this thread with the same basic symptom just follow this guide:
DirectAdmin Knowledge Base
docs.directadmin.com
Then take your time and be patient with setting all the records on your DNS whether you have your own or it is upstream with your server host.
Also, feel free to message me. I have made all of the most basic and silly errors possible so perhaps this could make me helpful.
Thank you all!