Blocking Constant Contact emails
On 11/17, Cox blocked the delivery of emails from my Constant Contact account sent to @cox.net addresses. Successful delivery to the same addresses happened a just a few days before.
The Constant Contact Delivery Support team informed me that I needed to authenticate CC emails sent using my domain, by adding two CNAME records to my domain's DNS:
If you're having similar problems, look at "Self-authenticate your email address" under your Constant Contact My Account -> Advanced Settings for guidance. Because DNS propagation can take up to 48 hours, Cox has prevented me from reaching my subscribers until the fix I apply compensates for their failure.