As a mail server administrator, setting up an antispam system is often my job. I used to use antispam proxy server aka ASSP and qpsmtpd as open source and free antispam gateways. However, setting up assp is a time consuming process, and it requires quite some cpu resource. Recently I started using postfix itself as an email gateway with postscreen and spamassassin. Here is my postscreen settings;
First, I needed to disable local mail delivery in postfix so that the emails will be sent to the actual mail server. Lets say we are going to receive emails for example.com. Our main mail server (zimbra/ms exchange/whatever) is called mail.example.com. We will call our antispam gateway/firewall ‘gateway.example.com’’.