This is really awesome, so awesome I think that you should think about how to monetize it and make some serious money. (I know that's seemingly against the "hacker ethos", but it's not often that you think of million-dollar ideas).
If I were them, I'd be scrambling to make recruiters pay $xx-$xxx to contact people through the site.
You should make it so recruiters pay when they get a response. The could only message candidates through the site initially (not via email) and their email would also be anonymized. If the candidate replied then the recruiter could be charged $XXX per reply.