policyd-weight is a mail filter for the Postfix

mail transfer agent The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...

(MTA) written in

Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...

. It allows postfix to evaluate mail envelope information and to score mail against several DNS-based Blackhole Lists (

DNSBL A Domain Name System blocklist, Domain Name System-based blackhole list, Domain Name System blacklist (DNSBL) or real-time blackhole list (RBL) is a service for operation of mail servers to perform a check via a Domain Name System (DNS) query whe ...

) before the mail is queued. The final score will determine whether a mail is rejected or accepted, in which case it is usually then subject to more resource intensive checks by a virus scanner and spam filter.

Features

policyd-weight works as a policy daemon in Postfix. It uses

, RHSBL, MX and A DNS queries of the

envelope sender {{No footnotes, date=June 2016 A bounce address is an email address to which bounce messages are delivered. There are many variants of the name, none of them used universally, including return path, reverse path, envelope from, envelope sender, MA ...

and HELO

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients ty ...

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 most installations of

SpamAssassin Apache SpamAssassin is a computer program used for e-mail spam filtering. It uses a variety of spam-detection techniques, including DNS and fuzzy checksum techniques, Bayesian filtering, external programs, blacklists and online databases. It i ...

Amavis Amavis is an open-source content filter for electronic mail, implementing mail message transfer, decoding, some processing and checking, and interfacing with external content filters to provide protection against spam and viruses and other ma ...

), 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 fewer

false positives A false positive is an error in binary classification in which a test result incorrectly indicates the presence of a condition (such as a disease when the disease is not present), while a false negative is the opposite error, where the test result ...

than

Sender Policy Framework Sender Policy Framework (SPF) is an email authentication method designed to detect forging sender addresses during the delivery of the email. SPF alone, though, is limited to detecting a forged sender claim in the envelope of the email, which is ...

(SPF) checks (example: blocked forwarders due to inconsistent SPF-records or passed Spam/Phishing due to Spam/Phishing-Domains with consistent SPF-records set).

Message flow

Please refer to thi
drawing

Licensing

policyd-weight is

Free software Free software or libre software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, no ...

, licensed and released under the

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...

External links

policyd-weight git repository

FreeBSD Ports

Mailinglist archive
{{DEFAULTSORT:Policyd-Weight Spam filtering Anti-spam Message transfer agents

Features

Message flow

Licensing

See also

Further reading

External links