I've used Rapportive to confirm if my guess of someone's email is correct. If you have the rapportive plugin installed, open gmail, compose, then type in the em

I've used Rapportive to confirm if my guess of someone's email is correct. If you have the rapportive plugin installed, open gmail, compose, then type in the email address in the To field. Then focus out and back in to that field (or just click), and Rapportive will try to find their profile info.