How badly do they want to get you?

I assume you would have taken precautions to not leave fingerprints on the envelope or the page? They can get the post office where you send it, but I don't see how they could get closer than that. There was some rumor that they could see microscopic IDs in graphics pages, but you're talking about text so I doubt that is possible. If the letter discusses your plans to blow up the White House, however, they might try pretty hard. If you're bitching about your neighbor they probably won't even read it. Nick withheld P.S. Do you enjoy living in a police state?