postgrey
Postfix greylisting policy server
Postgrey is a Postfix policy server implementing greylisting. When a request for delivery of a mail is received by Postfix via SMTP, the triplet CLIENT_IP / SENDER / RECIPIENT is built. If it is the first time that this triplet is seen, or if the triplet was first seen less than 5 minutes, then the mail gets rejected with a temporary error. Hopefully spammers or viruses will not try again later, as it is however required per RFC. The following features compared with greylist.pl from Postfix 2.1.1 are new: Safe database, automatic maintenance, whitelists, lookup by subnet, auto-whitelisting of clients, only Berkeley DB and no large mysql nor postgresql DB needed.
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