Spamilter is a Sendmail milter written entierly in C, and therefore
is faster and less cpu intensive than other interperative based solutions.

It blocks spam using the following methods;

    * Configurable Realtime DNS Blacklists
    * Sender Address verification
    * Configurable Black and White lists
    * Invalid MTA hostname verfication
    * Basic Virus/Worm file attachment rejection for files ending
      in .pif, .scr, etc.. via MsExtChk filter
    * SPF via libspf

Also;

    * Realtime firewall blocking of MTA hosts with invalid host names via
      MtaHostIpfw filter
    * Realtime rate limited connection blocking via firewall rule injection

All actions are logged via syslog with both the sender and the recipient.
From this, report generation and notification to recipients showing
 activity becomes extremely simple.

WWW: http://www.wanlink.com/spamilter/index.php