What is a DLR (delivery receipt)?
A DLR is the receipt a carrier’s SMSC returns for a sent SMS — DELIVRD, UNDELIV, EXPIRED — the only ground truth you get about whether a message actually reached the handset.
Definition
A Delivery Receipt (DLR) is the status report generated by the destination network’s SMSC after you send an SMS. Requested via the registered_delivery flag in SMPP (or a webhook in HTTP APIs), it comes back asynchronously — seconds to hours later — with a final state: DELIVRD (reached the handset), UNDELIV (rejected), EXPIRED (retries exhausted — phone off too long), REJECTD, or ACCEPTD (an intermediate “the SMSC took it” state that says nothing about the handset).
DLRs are essential and imperfect at once. Essential, because they are the only per-message ground truth for deliverability: delivery rates per route, per carrier, and per sender ID are all computed from them. Imperfect, because their fidelity depends on the whole chain — some routes fake DELIVRD to hide non-delivery (a hallmark of grey routes), some carriers return only intermediate states, and roaming handsets produce late or missing receipts. Comparing DLR patterns across routes is a standard way to detect both fake-DLR providers and dead number lists.
Why it matters
Without DLR analysis you are flying blind: paying for messages that never arrive, keeping OTP flows on routes that silently fail, and unable to prove delivery when a customer disputes it. A sudden shift in DLR mix on one route is usually the first visible symptom of a routing or fraud problem.
See it in action
Raw DLRs on every message via the SMPP gateway →