How To Opt-Out of Pre-Screened Credit Card Offers
OptOutPrescreen.com is the official Consumer Credit Reporting Industry website to accept and process requests from consumers to Opt-In or Opt-Out of firm offers of credit or insurance.
(From the Kim Komando newsletter):
This is one of those “How come no one told me sooner!” tips. You can stop preapproved credit cards and insurance offers coming to your physical mailbox with OptOutPrescreen.
Choose five years or forever. I picked forever.