If in the data sent across (via Apple servers) the IMEI and serial no of the device are also transmitted, then Apple can in that millisecond query on their various lists/inventories that this device is legit (activated device + IMEI + serial) and if all lights are green, proceed to deliver, otherwise drop it.

(perhaps different sets of data can be used, but it must be something that Apple already has, and the user has already provided (i.e. the iMessage email or the iMessage phone number, from the iPhone's enabled Settings)