Glossary
Related glossary terms
Email greylisting is a spam-filtering technique used by some receiving mail servers. When an email is received from an unfamiliar sender (i.e., a new IP/domain combination), the server temporarily rejects it with a 4xx error, signaling the sender to try again later.
Legitimate senders will retry delivery after a short delay, at which point the receiving server allows the message through. Many spammers and low-quality bots don’t retry, so greylisting acts as a passive filter for low-effort spam.
Key points:
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