Terminating Your Yahoo! Account page

Delete Your Yahoo! Mail Account

To delete your Yahoo! Mail or Yahoo! Mail Classic account:

• ›› Step by Step Screenshot Walkthrough
  

• Visit the Terminating Your Yahoo! Account page.
  
  
  
  • Sign in to your Yahoo! Mail account if prompted.
    
  
  
  
• Type your password under please confirm your identity with your password..
  
• Click Terminate this Account.
  
• Wait 90 days for Yahoo! to delete data (such as email messages) associated with your account.
  
  
  
  • Data connected to a Yahoo! Finance Premium account will be kept for 3 calendar years; other date may also be kept.
    
  • Note that your user name — and Yahoo! Mail email address — will be available for others to use in the future; they may receive messages meant for you if senders still use your old Yahoo! Mail address.
    In the meantime, senders trying to mail your deleted Yahoo! Mail account's address will get back a delivery failure message listing the account does not exist.
    
  
  
  
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http://email.about.com/od/yahoomailtip1/qt/Delete_Your_Yahoo_Mail_Account.htm

Closing your Yahoo account

We're sorry to see you go, but if you've chosen to close your account we'll show you how.

 Important:

   You'll need your current password to close your account. If you don't remember it, first use the Yahoo Password Helper to recover it.
   We recommend using a desktop or laptop computer. The web browsers on some mobile devices may not load all pages properly.

   Visit the Terminating your Yahoo account page.
   Read through the "Before continuing, please consider the following information" section.
   Confirm your password in the field provided.
   Enter the CAPTCHA code.
   Click Terminate this Account.
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https://help.yahoo.com/kb/closing-yahoo-account-sln2044.html