Why must we charge to filter spam?
The Evolution of SPAM
How it was:
In the past, hosting services filtered spam using the mail server's resources. Back in the days of Windows98 and even into the Windows XP era, this worked marginally well, but spammers have repeatedly defeated the mail server's defenses.
How it is:
In addition, this prevents the spam traffic from reaching the network where your domain is hosted, and your website is located. (Often the same network on which your mail server resides).
This configuration helps both your web server and your mail server to do their jobs, without interference from debilitating levels of spam traffic. It increases server "up-time", and drastically reduces system failure.