I have the same problem with POP3 on Windows Live Mail. Two phone reps told me they are getting calls on the problem but have no idea why. Another rep on the Cox app told me that Cox did maintenance on its emails servers this morning which why 3rd party email clients can no longer sync to receive emails, although emails can still be sent. But he said he did not have a clue how to fix the problem.
In short, Cox is telling customers to just use its WebMail and it is anyone's guess whether Cox will make the effort to fix its servers to once again allow 3rd party email clients to sync in order to receive emails.