Even a phone call does not guarantee lack of delivery -- it may come later or the administrator could miss it. Failure can never be proven. OTOH, if the administrator (or MessageStatus or end-to-end Ack) perceives a success, this should be definitive. Even for success, an end-to-end Retry may be necessary to get a required NRR (DR). Confirmation of non-delivery is not really possible (Logic 101 -- you can never prove a negative). TTL may come into play here and help resolve this but TTL is likely to be too long for time-sensitive issues. Regards, David Fischer Drummond Group.
