You can check to see if a Yahoo account exists either by using the account name availability checker or by sending an email to the account name. Yahoo accounts may be deliberately deleted or disabled over time; old account names can be made available again for registration. Use the availability checker before sending a test email to the account to confirm whether it exists.
The Yahoo account signup page will automatically check to confirm whether a Yahoo address exists. To check any particular account name, enter the name in the "Yahoo username" field and click out of the box. If the box does nothing, then the account name is not registered and does not exist. If the box changes to red and displays the text "This username is not available," it means that the account name is registered and exists.
You can check if a Yahoo account exists by sending an email to the related @yahoo.com email address. If the account doesn't exist, Yahoo will bounce back an email containing a 554 deliver error message that confirms that there is no account registered to that user name. If the account exists, the email message will either go through or produce another bounce-back message saying the account mailbox is full.
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