SMC Milter - Project Overview

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SMC Milter - Anti-Spam Email Filter

Protects email from spam and viruses, saving legitimate messages

Dear friends! This project needs your donation, even if it's will be a very small amount of money. Please support our project! Feel free to request new functionality with your donation. The current objectives of the project are listed below. The development team thanks you in advance for your support!

SMC Milter (mail filter abbreviation) - there is the plug-in for mail transfer agent (MTA). It is free software, distributed for free, developed for significantly reduce the amount of spam (junk-mail), that you recive. SMC Milter uses Greylisting like technonogy, for junk mail blocking and set of original automatics algorithms "White listing", for detecting legal but unknown senders. In order to viruses protection SMC Milter uses Clam AntiVirus.


SPAM - is anonymous unsolicited bulk e-mailing, usually with advertising. According to available statistics, the global ratio of spam in mail traffic is about 80%, and many consider the problem of spam kind of overwhelming disaster. A phenomenon which although can be more or less effectively oppose, but from which it is impossible to completely get rid of principle. This happens because to date there is not only no "standard" methods of spam filtering, but the generally accepted approaches such filtering. In other words, the same letter (with the same text and technical information) can be seen as spam by users, and some as non-spam - other. At the same time, server anti-spam filters can not make assumptions about the wishes of the recipient and are forced to make a decision on classification based only on technical information and the message text. Any anti-spam filter has a certain number of false positives, thus could be losing important business letters. This means that the spam problem can not be effectively solved only programmatically. Thus, the fight against spam should be divided into three stages: prevention, detection and punishment of the source of distribution for the offense. Legislative measures are already in many countries make it possible to apply for a spammer and his client to court and ask them to compensation for material and moral damage. At the same time, it is necessary to adopt a series of measures designed to prevent spam. Today used mail transfer protocol SMTP/ESMTP (RFC 2821) has a number of significant drawbacks. Initially, SMTP does not support a single authentication scheme. As a result, spamming has become a virtually unsolvable problem, since it was impossible to determine who really is the sender of the message - you can actually send a letter on behalf of any person and the task of finding the source distribution becomes very difficult. Currently, attempts are made to solve this problem with the help of specifications SPF (Sender Policy Framework), Sender ID, Yahoo Domain Keys. Unified specification currently does not exist.


The spam problem is solvable. Legislative measures are already possible in many countries to apply for a spammer and his client to court and ask them to compensation for material and moral damage. Unfortunately, SMTP mail transfer protocol being in use today does not always allow to identify real message sender with responsable accuracy. The method we offer consists in analysing the possibility of identifying real message sender under the existing SMTP protocol. A letter is considered trustworthy if actual sender is known or can be detected easily. Based on this idea we have designed AutoSPF, an efficient message sender verification system, and SMC Milter, junk mailing (spam) protection system implemented in the form of plug-in for milter API supporting popular mail transfer agents (MTA).

SMC Milter project has been developed since 2003. By default the filter uses Greylisting technology to block junk e-mail, and a suit of automatic "white lists" working with original algorithms to determine legal e-mail which would be delivered without delay. SMTP authorising and blocking all Failed e-mail are supported. Since 2.0 milter version was added Postfix and ClamAV (clamcheck configuration file parameter) support. The policy of e-mail "legality" determining (message sender verification) by default uses AutoSPF and SPF algorithms.

Current project chellanges

  • Implementation "Spam URL Realtime Block List (SURBL)";
  • Stream mode using ClamAV;
  • Rename-function for "unsafe" files formats .

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