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 ago, then the mail gets rejected with a temporary error.
(Greylisting is a method of blocking significant amounts of spam at the mailserver level, but without resorting to heavyweight statistical analysis or other heuristical (and error-prone) approaches. Consequently, implementations are fairly lightweight, and may even decrease network traffic and processor load on your mailserver).
Features include:
- Safe database.
- Automatic maintenance.
- Lookup by subnet.
- Whitelists.
- Auto-whitelisting of clients.
Website: postgrey.schweikert.ch
Support: Tutorial
Developer: Open Systems AG
License: GNU General Public License v2.0
Postgrey is written in Perl. Learn Perl with our recommended free books and free tutorials.
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