SpamAssassin has a high spam detection rate, but despite this, some spam emails always escape detection. Conversely, legitimate emails are sometimes marked as spam.
This chapter looks at whitelists and blacklists—techniques for spam filtering that mark known good and bad senders. We then discuss the situation where emails have been wrongly classified, and how to resolve this by altering scoring on rules. Finally, we discuss filtering out certain foreign languages and character sets as a method of reducing spam.
SpamAssassin works very well at detecting spam, but there is always a risk of false positives or false negatives. By using a list of email addresses that are known spam producers (a blacklist), email from spammers who use consistently use the same email addresses or domains can be filtered out. With a list of email addresses that are legitimate email senders (a whitelist), emails from regular or important correspondents are guaranteed...