Delivery reporting is a feature of SMS MT that reports back if the SMS message has been delivered, for every message sent. It is sourced directly from the handset.
Essentially, DLRs are URL call-backs for Delivery Reports. Instead of the gateway logging the activity, it will call-back the provided URL using a query string (at the end) with the parameters of the delivery report itself.
Descriere
Ref:
http://api.i-digital-m.com/v2/documentation#send-sms
https://www.infobip.com/en/glossary/dlr-delivery-reporting