Have you already follow these steps?
Contacting Cox for Assistance
If you are having problems with email delivery to Cox, and you were unable to resolve your problem using the steps in the Error Codes section above, send us an email at email@example.com for assistance. Your email must contain all of the following information in order for us to process your request.
IP/CIDR range of outgoing email servers
From the following choices, indicate the item that best describes the issue you are experiencing.
My IP address is being blocked
My domain is being blocked
My email is being marked as spam
My email is not arriving to the intended recipients
My email is being delayed
Include a detailed description of the issue you are experiencing, such as the date and time when the problem began and the corrective action that has been taken.
Include email server logs related to the issues.
Note: Due to the technical nature of the requested information, this email should be submitted by an email administrator or other technical contacts that is familiar, and can obtain, all of the requested details.