This doesn't answer the question directly, but I've been keeping a list of JIDs that I've seen sending spam:
https://bitbucket.org/snippets/SamWhited/rLqKB/spammy-jids Feel free to add to it (I think you can do that with snippets? If not I'll move it to a wiki page). I'm probably just going to start blocking any server that has open registration which doesn't require at least a captcha. —Sam
