If you delete a message from Inbox, then it moves into the Trash folder, but if you delete a message from the Trash folder then emails deleted forever from your Yahoo mail account. But, there is a backup created, from here you can restore it from any 60 days. If Yahoo Mail Down, then it only stops to access this site for a few times, not more. https://www.contact-customer-service.net/blog/yahoo-mail-down/