Don't Permanently Delete emails - Legal Reasons
Yahoo must not automatically permanently delete emails from inboxes if the account remains unused for long period. It must follow example of gmail which retains emails/inbox material at least for 2 years before deleting it permanently. Sometimes, emails deleted by yahoo are very very important for the user since these emails may be needed to be produced as evidence in a court of law in legal matters. The user must be given the option if they want to delete Or retain emails in inboxes for long.

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If your account has had no activity for 365 days, then the account is deactivated. We communicate this a few times which includes sending you an email to your alternative email account, so make sure that is updated. If you need help reinstating, contact our CC team at help.yahoo.com. They have the tools to help with these issues. Hope this helps!