email address

I've not heard of email addresses being ported, phone numbers sure.   Have you asked them to see if your email address is available with a cox.net domain?   Once they make the 1st cox.net you can make additional ones yourself

Basically email addresses are unique to each provider so they cannot be ported.  You would either need to make arrangements with AT&T to maintain access to your old email account with them or create a new email address with us or another email provider of your choosing.