DoS the spammers

How does one stop spam? I don't think it's possible to entirely stop it. But it could be possible to make it less interesting, or at least less easy. DoS the spammers. Of course, preferably without DoSsing yourself.

I'm thinking about setting up something like the following:

1. Make sure I use SMTP-time spam filtering.
2. Write an application 'throw-junk-back' or something that will take an IP address on the command line and a bit of data on stdin, that will pick five random numbers between 1025 and 65535, and that will send the stdin data to the IP given to it on the UDP ports with the numbers we generated.
3. When we're quite sure that what we received was spam (in case of spamassassin, when the score is above 15 or so), pipe the mail to 'throw-junk-back' with the IP of the connecting system.

If everyone would do this, then spammers will require four or five times their current bandwidth (not six times, because UDP has less overhead than TCP, and there'll also be false negatives), which is going to cost them a /lot/ of money, whereas it would not really hurt people that get hit by false positives (provided that only happens once or twice).

Is that a good idea, or am I crazy?