Nice tutorial to build Anti Spam Gateway in OpenBSD.
This document describes how to setup a spam-blocking email gateway based on open source and freely available software. This procedure is designed for a small to medium sized company. It describes how to setup a new computer that is meant to run on your network’s DMZ in between the Internet and a corporate email server like Lotus Notes or Microsoft Exchange.
The tutorial uses the following software:
Operating System: OpenBSD
MailScanner & Antivirus: Amavisd-new, SpamAssassin, Razor and DCC