dave@turbocat.de (David Wetzel) writes:
> I do a DNS name lookup on all host that send mail to me. And It
> works well for computers with dynamic IPs. All serious ISPs will
> have a working reverse DNS entry for all IPs they use.  If DNS is
> not working, it is very likely that is is spam.

In addition if you test the validity of the HELO hostname, you will
catch a few more of the miscreants.  Instead of figuring out how to do
this is in sendmail, I switched to postfix which has that and a few
other useful anti-spam tests as simple switches one can turn on.

A slightly edited version of my anti-spam checks are online at:

        http://www.wsrcc.com/spam/

-wolfgang
-- 
The cpu is willing but the powersupply is weak.

spider food: http://www.wsrcc.com/baddream/usenet/
(NOTE: The email address above is valid.  Edit it at your own peril.)