Install SpamAssassin on CentOS for Axigen

yum install spamassassin
service spamassassin start
chkconfig --levels 235 spamassassin on

In WebAdmin enable SpamAssassin

Go here and set up required rules http://www.yrex.com/spam/spamconfig.php

Copy output and paste into:

vi /etc/mail/spamassassin/local.cf