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Greylisting — an anti-spam technique that temporarily rejects an unfamiliar delivery attempt with a transient SMTP response and accepts a legitimate sender's later retry.
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.
Greylisting — an anti-spam technique that temporarily rejects an unfamiliar delivery attempt with a transient SMTP response and accepts a legitimate sender's later retry.
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.
