I use a RBL on my mail servers and a filter on my workstation e-reader. add them to the filter. Clicking anything on the page or even allowing the images in the email to load ( fire wall won't let my email program access anything but 21.25 and 110 ) will tell them you looked at it. check the image properties on your next spam...
http://www.yourspammer.com/email_sca...urdomain .com