postgrey: postgrey (Postfix Greylisting Policy Server) postgrey: postgrey: Postgrey is a Postfix policy server implementing greylisting. When a postgrey: request for delivery of a mail is received by Postfix via SMTP, the postgrey: triplet CLIENT_IP / SENDER / RECIPIENT is built. If it is the first postgrey: time that this triplet is seen, or if the triplet was first seen, less postgrey: than 5 minutes ago, then the mail gets rejected with a temporary postgrey: error. Hopefully spammers or viruses will not try again later, as it postgrey: is however required per RFC. postgrey: postgrey: You need to have postfix installed and configured to install this.