After a bit of searching, I think I have finally found the location to stop getting all of the credit card offers from Chase (United Mileage Plus Credit Card Offers).  We’ll see if it works.
After going to http://www.dnmoptions.com, I was presented with a page from Chase to add my address and remove myself from their mailing list .. We’ll see if it works, hopefully you will have success as well.
After submitting my request, I received the following response:
Your mailing options have been submitted. Your options will remain in effect for …