Write to:
Mail Preference Service
Attn: Dept 12732061
Direct Marketing Association
PO Box 282
Carmel, NY 10512

Or go to this link: http://www.dmaconsumers.org/cgi/offmailinglistdave

Ask to opt out of national mailing lists. It's free to register by mail, faster (and $5) to register online. Either way you should see all junk mail drop off to a trickle within a couple of months. I never receive anything from AMEX outside of my statements and the occasional letter. I don't get much other junk either.