Hi Bridgeguy,
It sounds like they could be blocking us as possible spam, and not allowing the message to go through. It could also be the IP address that you are sending from, I can look up your IP to see if it is being blocked as well. Have you tried sending from a different e-mail address (if possible), that would narrow it down too. If you could e-mail me at coxhelp@cox.com with the IP address I will look it up for you.