Delivery report (DLR)

The carrier's confirmation that an SMS reached the destination handset, or an error explaining why it did not.

A DLR is the receipt of the SMS world: the destination network reports back that the message was delivered, is pending, or failed. Senders use DLRs to trigger retries and fallbacks (like voice OTP).

DLRs can lie on poor routes, reporting delivery for messages that were filtered, which is why serious measurement counts codes actually entered by users rather than DLRs.