When we learn more about how anti-spam filters operate, we can get much closer to an answer to this question.
Email messages are reaching the mail server of our addressee. However, before the messages are saved in a particular inbox, an anti-spam application will analyse the message, and categorise it. The most popular solution used by anti-spam software is to carry out some tests, and each test ends with an allocation of a specific number of penalty points. Email will be considered spam when the anti-spam filter will allocate a certain number of penalty points to it – equal to or higher than a set limit (most frequently, the limit is 5). There are a number of tests available. They are of different significance (by number of allocated points).
Currently the most popular tests, and of the highest significance, are testing the email source; a so-called Baesian filter is also widespread. The Baesian filter is a remarkable tool, as it is a self-learning filter. It analyses the content of emails by words that frequently appear in spam messages. Each Baesian filter is operating independently – as a result, there are no email marketing mechanisms that could evaluate the probability if an email will be classified as spam.
