failures verifiedimportant

This is the number the console pairs with deliveries to make its rates, so its composition decides what every percentage on the screen means. Eleven of the thirteen error counters go into it. The two left out are unassignable — messages that could not be matched to a sending address — and strange, the engine's own bucket for what it cannot classify. Both of those are failures by any reading: the message was not delivered, and it will not be retried into existence. Leaving them out means deliveries + failures is not the count of finished messages, and a success rate built on it is slightly generous. On a healthy node the difference is invisible; on a node with an address misconfiguration it is exactly the problem being hidden. For our own charts the rule follows from our own standard — the parts must sum to the whole. We compute our own total from the individual counters rather than taking this one.