MAKE THE NEW SIGN-IN PROCESS THE SAME AS THE OLD. it'S CURRENTLY iMPOSSIBLE.
New E-mail: You need an authorization code to log in to your new e-mail BUT you send that authorization to the e-mail. You can't access it to SIGN IN without BEING Signed-in to access it. Has anyone thought this through???
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If you're having account or sign-in issues, please contact our Customer Care team at help.yahoo.com. They are separate from the Yahoo Mail team. They resolve these types of issues and have the tools to help. Hope this helps. Thanks!
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SME commented
You can add more recovery options for verification like cell number and an alternate email address like another Yahoo, Gmail or Outlook. The more recovery options, the better.