Before 2017 users can't access an Att Email Login account with Yahoo mail ID. In mid-November 2017 you can log in to att.net with Yahoo mail ID. Both Yahoo and ATT have differentiated themselves and are now offering the services. To login into ATT.net, you must use your AT&T email account instead of your Yahoo email address. Login in with your AT&T email address to access your AT&T account through my AT&T or Att.Net Email Login Page.
Also Here: Log In To Your Windstream Email Account
Also Here: Log In To Your Windstream Email Account