Definition
A delivery receipt (DLR) is a status message returned by the operator network that tells the sender whether an SMS was delivered to the handset, expired, or failed, along with timestamps and an error code.
In SMPP v3.4 the sender requests a receipt with the registered_delivery field of submit_sm. The SMSC later returns it as a deliver_sm whose esm_class marks it as a delivery receipt.
The SMPP specification gives an example receipt text (Appendix B) with fields id, sub, dlvrd, submit date, done date, stat, err and text, and final states such as DELIVRD, EXPIRED, DELETED, UNDELIV, ACCEPTD, UNKNOWN and REJECTD. The exact format is SMSC-specific, which is why providers normalise it.
An HTTP API usually exposes the same information as webhook events, for example SENT, DELIVERED or FAILED, mapped from the operator receipt.
Limits: some operators return no receipts or return them late, and some return “delivered” when the message reached the network rather than the phone. Treat DLRs as strong evidence, not proof of reading.
Example
id:7f3a91c2 sub:001 dlvrd:001 submit date:2610101030 done date:2610101030 stat:DELIVRD err:000 text:Your code is