📖 Glossary
What is Greylisting?
An anti-spam technique where a receiving mail server temporarily rejects emails from unrecognized senders, asking them to try again later.
Detailed Explanation
When a receiving server employs greylisting, it temporarily rejects an email with a 4xx "try again later" response. Legitimate mail servers are designed to retry delivery after a delay (typically 15 minutes to an hour). Spammer software, often optimized for speed, usually does not retry. Thus, greylisting effectively blocks a significant amount of spam without permanent loss of legitimate mail. For email verifiers, greylisting can cause verification delays.
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