individual critical
One message or the whole domain
Whether the failure concerns this message alone or everything going to that destination.
In detail
The distinction that separates a dead mailbox from a blocked sender, and it is given rather than guessed. A per-message failure means the address is bad; a domain-wide one means the receiver is refusing us, and no amount of list cleaning will help. For analytics that is the difference between "clean your list" and "you have a reputation problem" — the two recommendations a deliverability view exists to tell apart.