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NDR — a Non-Delivery Report that informs the sender or submitting system why a message was not delivered.
Deliverability is determined by a combination of SMTP results, IP and domain reputation, list quality, complaints, content, and SPF, DKIM, and DMARC checks. No single metric guarantees inbox placement.
NDR — a Non-Delivery Report that informs the sender or submitting system why a message was not delivered.
A receiving server can use this signal when accepting, temporarily deferring, rejecting, or filtering a message. Its weight depends on the recipient’s local policy.
Correlate the SMTP code and rejection text with sending logs, reputation, complaints, and authentication results. Remove invalid addresses and do not retry indefinitely after a permanent failure.
