Policyd-weight
From Wikipedia, the free encyclopedia
policyd-weight is a mail filter for the Postfix mail transfer agent (MTA) written in Perl. It allows to evaluate mail header information and to score mail against several DNS-based Blackhole List (DNSBL) before the mail is queued. The final score will decide whether a mail is accepted or rejected before it is subject to more resource intensive checks by a virus scanner or spam filter.
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[edit] Features
policyd-weight works as a policy daemon in Postfix. It uses DNSBL, RHSBL, MX and A DNS queries of the envelope sender and HELO SMTP arguments to evaluate the possibility of either forgery or spam. Rejection happens based on an overall score, so a single blacklist entry may not cause the mail to be rejected. The score is determined by various checks and is not linear. The administrator is able to adjust scores for each check to meet her requirements. policyd-weight caches the most frequent queries to minimize bandwidth and CPU usage.
The benefit of this approach is that it is able to reject a delivery attempt before the body (DATA) of the mail has been received (unlike SpamAssassin or amavisd), thus saving network bandwidth. Also it does not add delays like Greylisting and keeps out clients which fake HELO or sender information with a better accuracy and less false positives than Sender Policy Framework (SPF) checks.
[edit] Message flow
Please refer to this drawing.
[edit] Licensing
policyd-weight is open source, licensed and released under the GNU Public License by Robert Felber (Ford München - Kuttendreier.de).
