Well, if you are a Yahoo and AT&T user, then you must have a merged account. Most people don't know why and how it happened that you started using your Yahoo or AT&T username and password to login into your account.
You must know that since the partnership between Yahoo and AT&T was formed, the email accounts were merged together. If you had email accounts on both the platforms, the accounts were merged into a single one and keeping both inboxes. So, now your Yahoo mail redirects to AT&T inbox or vice versa.
After that, even passwords were the same for both accounts, and users had to use the Yahoo mail login platform to log in to their account. But in September 2017, they decided to unmerge AT&T Yahoo mail into two separate accounts.
So, it means now you have a choice to unmerge the account at your will. If you want to keep using both accounts as they are, you can do that. If not, you can use the unmerge feature and separate both accounts.
Open onlinegeeks.net in your web browser to learn more about the Yahoo mail, and AT&T merged accounts and how to separate them.
Few questions search by Yahoo AT&T users-