SpamAssassin is a popular anti-spam program. It is run on the server and checks all emails as they come it. It looks for a large number of different aspects, and then gives each email a score of how likely it is that that email is spam. If the score is above a certain number, then SpamAssassin can place that email is the spam folder, or delete it altogether. This depends on how SpamAssassin is setup.
It is possible to add whitelists and blacklists, and to change the way the SpamAssassin scoring mechanism works. For example, it is possible to add points if an email contains a certain word or if it is from a certain domain, or even from a certain country. The beauty of SpamAssassin is how configurable it is.
But even without any configuration, SpamAssassin is very good at figuring out what emails look like spam and which emails are legitimate. However, if you notice that you are receiving a lot of spam, you can easily make the settings of SpamAssassin be more strict.
The best way to do this is to lower the default score that an email gets before it is considered spam. To do this, edit your ~/.spamassassin/user_prefs file. Inside this file you will see a numeric score. The default is a 5. You can make SpamAssassin more strict by lowering this score. This score is the amount of points an email can have before it is marked as spam by SpamAssassin.
The lower the score, the more strict SpamAssassin will be. If you are just setting up SpamAssassin and want to test to make sure that it is working, you can set this score all the way down to 1. That way every email sent will meet the spam threshold, and will be considered spam. If you do this, be sure to set the score back up to 5 or whatever you need it to be.
Of course, the same is also true. If you find that SpamAssassin is acting too strict and marking too many legitimate emails as spam, you can change the default score to 6 or higher.
This is a quick and easy change to how strict your anti-spam filter will be. By default, SpamAssassin has a good scoring system. Unless my users are getting a very specific type of spam, I will play with this score before adding any custom rules.
