Account recovery is the worst I have ever seen.
I work for a telecommunications business and I often have to help with email issues. I have never experienced such incredibly unfriendly account recovery process. Many seniors have issues adding recovery emails or phone numbers to their accounts, Especially if the account was made over 5 years ago. This creates large issues. Yahoo's policy is "too bad so sad" if you forget your password and have no recovery options. This is ridiculous, People have countless things attached to their email and often need access to said email in order to change it. They are then screwed with any other services attached to that email.
Change your recovery process. It's laughable and frankly embarrassing for such a large and well know email service.