We are conditioned to think of spam as a bad thing. What if we really wanted to make a statement about warrantless monitoring of Americans’ communications? Yes, we can encrypt our email, but frankly, except for some folks on the tin-foil-hat margin (which doesn’t seem quite as marginal these days), usually the people who are using strong encryption actually have something to hide. And when only those who have something to hide encrypt, it really makes it easier for the NSA to focus their resources. Moreover, much can be learned by traffic (who sends to whom, even without the “what”).
Using, for example, PGP is not enough. You need to use PGP to encrypt a message for that special someone, and then send the email to everyone you know and a few thousand you don’t. This pool that you send to can be randomly assigned (beyond your real contacts) and shift slightly with the addition of a few dozen new random email addresses every day, so as to disguise real new contacts.
There are plenty of downsides. Total email traffic would go through the roof. Spam is bad enough now with–really–a fairly small number of spammers. I can see this choking mail servers pretty quickly. If you got everyone’s email, that would be a bad thing, so you would want to set up overlapping communities of recipients. And of course, you would need the recipients to opt-in to receiving encrypted spam.
I have to assume that at least some of the spam I receive every day is just this: steganographic broadcast of private messages. But it seems to me that we could all use a little privacy in our electronic communications these days.
Extending a mail reader to work with this would be simple enough. Try to decrypt every email coming in: if it comes up garbage, trash it. Heck, as long as you are extending the reader, you could make it capable of forwarding encoded messages, adding an additional layer of obscuring noise.