Is there a US government authority you can contact if you want to stop all junk mail?

No there isn't. Junk mail as you know is just a form of advertising. You should try going on a good anti spyware such as free AVG off the web (I use it.) Go on Type in: Free AVG anti spyware The downloading is simple and it will automatically up-date itself on your computer. The best of all IT'S FREE! * There is no US governmental agency but a consumer wishing to be removed from junk mailing lists of any type (US Post, emil etc. and telemarketer list, etc.) can find the information for doing so at Consumer Assistance Direct Marketing Association site.