I have been a customer of Cox since 2011 (Internet, cable and home phone).
I have always (since 2011) relayed my outgoing emails through smtp.cox.net
I have encountered only a few problems ... until recently. Over the
course of the last five or six months smtp.cox.net has been down or has
not recognized my password many times. Also, there has been many times
over the course of the last five or six months where an email I have sent
has been returned to me accompanied by a cryptic error message. And there
has even been times where my outgoing emails have not been relayed, and I
have not been alerted to such with an error message.