Delivery Error clarification

Hello. One of our recent emails had quite a few "delivery errors". When I went in to look more closely, the Reason Details says "Reason details: Sending failed and all attempts to resend failed" 



While it's clear the sending failed, there's no detailed context as to why it failed (i.e. Invalid email, unsubscribed, etc). Please advise on how to gather more concrete and detailed data. Thanks.