Greylisting: What It Is and How It Affects Email Delivery

Greylisting is an anti-spam technique where a receiving server temporarily rejects an email from an unknown sender and expects the sender to retry later. Many spam systems won’t retry correctly, so greylisting filters them out.

Legitimate senders should retry automatically with backoff. If you see frequent greylisting, ensure your MTA retry settings are correct and your sending reputation is healthy.