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Story: Using a five-layer filter to cut spam

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The strategies used by this company are interesting. But, as is always the case, there are better solutions. We are publishers of an agricultural commodity market news service, with customers in 60 countries. We recently solved the problem of having our website spidered for email addresses by creating a form -- similar to this -- and a perl script to manage the input. The page contains no javascript and is therefore compatible with all browsers and users behind forewalls report no problems. We had been receiving over 500 spam emails per day. We eliminated almost half the spam by carefully reviewing the email addresses which were being used to reach us and removing those which are not commonly used from our mail server. For the balance, we use a server based solution -- a antispam filter system we created which scans all inbound messages received on our Mercury32 mail server. On average, no more than 10 messages get past the filters, and all that do are used to generate new rules. Companies which have installed our system on their Mercury32 mail servers report similar results -- eliminating between 95% and 98% of spam each day. We deal with email viruses in two ways. We deny messages which have attachments which are obviously executible content. We then use AVG antivirus to scan all messages with attachments which make it through the prefiltering phase. This has been close to 100% effective and often traps new email viruses before anti-virus definitions have been created. We would love to figure out how to trun our system from a freely available one to one on which we can make money in order to recover the cost of maintaining the filter set. However, we will not stop working on the filter set because it ha proven extremely effective for us and for the companies which are using it to combat spam in their systems. The filter is available for download from http://www.stat-communications.com

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