A non-delivery report is a bounce message explaining why an email didn’t reach the recipient.
A Non-Delivery Report (NDR) is the message you receive when an email fails to deliver. It often includes SMTP codes and diagnostic text that indicate whether the issue is permanent (hard bounce) or temporary (soft bounce). For email automation, NDRs should feed directly into suppression and retry logic. Understanding NDRs helps teams clean lists, identify blocks, and spot misconfigurations quickly. A good glossary entry also explains common codes, what actions to take, and what to avoid doing next.