Beyond the existing mobile push sent metric, it would be good know if the push message was delivered to the device and if not, why not. Having a sent metric is fine, but how can a marketer tell if the message was delivered, open and read, delivered and not read or not deliver at all because the app has been deleted, notifications are disabled, customer has opted out, DND, OEM/GCM related, GCM/FCM connectivity related, GCM/APNS errors. A delivery metric is needed.