DNS greylisting to lessen the amount of incoming spam.

Greylisting is a technique for slowing down the oncoming torrent of spam on the Net today by breaking spamware that isn't compliant with the SMTP RFCs. It consists of a simple alteration to your DNS zonefiles that places an IP address that doesn't have anything listening on port 25/TCP in the position of your primary MX, and the addresses of your real MX's in positions of lower priority in you DNS zone. Spamware that isn't compliant looks at your DNS records for the IP address of the primary MX, tries to contact it, fails, and gives up, or at …

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