How does AVS Antispam Prevent from Spam?

AVS Antispam provides the superb protection from spam due to five filters:

• Heuristic filter. This is the rule based filter. The rules (nearly several hundred altogether) are pre-defined and serve a certain area in the email structure. The rules check if, for instance:
• weird symbols repeat in the email body;
• 80-90% of lines in the email body are blank;
• the email header has an invalid date (e.g. non-existing time zone);
• the email subject talks about money reward;
• the email message text is disguised using an additional encoding, etc.
• Statistical filter. This filter is pre-trained initially and as the emails are marked as "Spam" or "Not spam" manually the statistical filter enriches its spam sign knowledge. The filter knowledge is presented as a database that contains words and associated with them numeric coefficients specifying the probability that a word is attributable to junk email. When an email is handled with the statistical filter each word of the email is checked on presence in the database. If a word is found, its numeric coefficient is used to calculate the word contribution in treating the email as junk by means of the Bayes' formula. Then, such word contributions are summarized to get the email total spam value which is compared with a certain threshold value to make a final decision.
• Realtime black list of IPs. This filter checks presence of the message sender IP address in remote black lists that are published on hosted nameservers. Such black lists are expanded in several ways, for instance, by a nameserver owner manually, by an anti-spam server software that detects the spam sender IP address and add it to the remote black list, by users who mark suspicious messages as spam when use the web based interface from a mail service provider rather than an e-mail program.
• Realtime black list of URIs. This filter is similar to the previous one excepting it checks the email for spammer URLs using the corresponding remote black lists.
• Black and White lists. This filter is customizable because you define the untrusted and trusted sender e-mail addresses by yourselves. The filter enabled (Use black list or Use white list is checked) with addresses added overlaps a decision made by any other filter, in other words it has the priority over others in such a case.