SMS & SMPP
Ref: SMPP v3.4 Section 4.5.1 deliver_sm
DLR
Delivery Receipt
Direct Telecom Definition • Carrier Industry Standard
An asynchronous network status notification confirming whether an SMS was delivered, buffered, or rejected by the handset.
Technical Definition & Carrier Engineering Standards
DLRs are returned via SMPP deliver_sm PDUs or HTTP webhooks containing standard error codes (e.g., DELIVRD, UNDELIV, EXPIRED) reflecting true Mobile Switching Centre (MSC) or Handset acknowledgement.