It's not uncommon for e-mail users to forget their password, particularly if it is frequently changed. However, most e-mail users rarely forget their e-mail address or sign in ID. If you have forgotten your Yahoo e-mail address, you'll be unable to sign in to your account. Fortunately, there is a way for you to determine your address so you can locate your e-mail account and sign in.
Visit the Yahoo Mail ID Help Center by going to edit.yahoo.com/forgotroot. Select "I Forgot My Yahoo ID."
Click "Next" to enter the second stage of the recovery process. Type your alternate e-mail address. This is the alternate e-mail address you provided when you signed up for your Yahoo Mail account.
Type your date of birth, ZIP code and country of residence. Click "Next." The system will provide you with your Yahoo ID. Return to the main Yahoo website and sign in using your Yahoo ID and password.