Those DNS servers are all owned by COX, so if you switched from them they won't work, if you switched to them they will.
IPv4 is preferred over IPv6
Static is best.
As for gmail
smtp.gmail.com on port 587
Encryption should be STARTTLS, and NOT the STARTTLS (If available)
But none of that applies to your ISP. So the gmail issue would either have to be separate, or you are using a relay SMTP server hosted through the non-cox ISP.