Maybe a scam or maybe not. If the date/time on your computer is incorrect, the server will assume your certificate has expired.
However, with the latest barrage of email complaints, it could be an issue with the certificate on the Cox server.
If the connection between you and Cox has changed to SSL, you'll need to reconfigure your browser or client. Or you may need to update your browser or client to accept whatever SSL certificate Cox is using.
However, if the intent of the email is to get your credentials or to click a link, it could be a scam.