Greylisting
Greylisting is an email anti-spam technique that temporarily rejects incoming emails from unknown senders, requiring them to be resent after a delay. It works by leveraging the fact that many spam-sending systems do not retry delivery, while legitimate mail servers typically do. This method helps reduce spam without relying on content filtering or blacklists.
Developers should learn greylisting when building or maintaining email systems, especially for small to medium-sized organizations or personal servers where spam is a concern. It's particularly useful as a lightweight, low-maintenance first line of defense against spam, complementing other techniques like blacklisting or content analysis. Use cases include mail server configuration (e.g., with Postfix or Exim) and enhancing email security in applications that handle incoming mail.