Neat idea. I know it's not a serious proposal, but the problem with this sort of approach will be that the message will be identifiable from the fact that it hasn't actually been sent as spam to many people. So an attacker can identify a suspect message just by considering its distribution.
So why not send it as spam? The key here is hiding in the this can be done in multiple ways.
1. Encode fake spam and send spam thousands of people with it.
2. Also send lots of real spam to your intended targets.
Their spam filter could then attempt decoding and identify the fake spam from the real spam, and you just look like a big nasty old spammer.
The thing I like about this approach is that for all we know, it's used already, and some of those junk emails that we've got, you know, maybe even a classic, could have actually been messages from some spy agency that contained a message!
Depends on how you define "harm" i suppose. Considering it's not real spam, there's not a real scam company on the other side of the message waiting to grab your cash, the "damage" is a few hundred kilobytes of text ending up in the spam can along with all the other legitimate spammers.
