Spam Filter for ISPs is designed to be a front-end for your incoming SMTP server. It receives all emails addressed to your domain(s) and checks if the sender is listed in one or multiple DNS-based block lists; if not, the email is passed on to your main SMTP server. The administrator can configure which block lists to use, set allowed domains, filter by keyword and maintain a blacklist as well. SpamFilter runs on Windows and Linux systems, both distributions are included in the download.