Default SMS Delivery Notifications to on
 

Default SMS Delivery Notifications to on:

To always have SMS Delivery Notifications enabled:
HKCU\Software\Microsoft\Inbox\Settings\SMSDelivery Notify = 1 (DWORD decimal)
To disable them (can still enable per-SMS in SMS settings):
HKCU\Software\Microsoft\Inbox\Settings\SMSDelivery Notify = 0 (DWORD decimal)

Note that SMS Delivery Notifications are a network provider option, and the recipient may refuse them to be sent out