How to stop certain spam?

[Remco Barendse]

We are getting flooded with messages from one particular advertiser. The 
send dozens of messages each day, all in similar format, a few lines of 
invisible text and some images with their spam crap.

On the right side in the image i often get some crap message like : Sorry, 
this advertiser is not available

The messages hardly score on Bayes and they are never caught by the 
blocklists i use bl.spamcop.net cbl.abuseat.org dnsbl.njabl.org 
chinanet.blackholes.us zen.spamhaus.org

The messages usually are awarded some points for DCC and Razor2 checks.

There is always some USA postal address written at the bottom.

A lot of messages are about auto insurance, some satellite dish offers and 
auto insurance.

Because every message contains url's to a different (new) website i 
unfortunately am not able to give a more precise description.

How to stop this?

Thanks!!