Yahoo!/ATT email authentication not functional

sbcglobal.net email domain - authentication stopped working at 22:20CT on Sat 7/13. att.net domain was functional until 9:00CT on 7/14. Error message - Sorry we cannot process your request." Tier1.5 issued pin# resets, cleared cache, tried both IE and Chrome browsers. Current status for sbcglobal,net email account is "too many user attempts." It was explained Tier2 is working a known email authentication issue. And that I would have t to call in after ATT email issue resolved to have my email account unlocked. In the meantime, other mail users report getting rejects for emails sent to me.