this is easy, yahoomail is designed in such a way that, if umistakenly delete a message, or even if u intentionally delete a message, it will be deleted from ur inbox, but there is sometin called trash, all the deleted messages are usually stored in the trash
but in a situation where u cant find the message both in trash, spam or inbox, u will have to mail MPNP and tell them ur file number and the problem ur having, also give them ur email, and if there is no responce, call them,