I think it is the fact that I had the SMTP server on the host OS and not some where else, I did some reading about the no route to host issues I was getting from Docker and Firewalld. What I put as the steps I did to get it working was what I read.
Granted as I said the knock on affect of doing what I did was the fact that I need to add all of the required ports in the trusted zone.
It seemed to be the only way I could get what I wanted working.
Cheers,
Rei