title: Web service to check existence of email?
body: <p>I have my little web application, with simple registration strategy - provide email and password and you are done.</p>
  
  <p>Recently bot's starting to attack my application, registering big number of users from non existent emails using the same passwords. </p>
  
  <p>I want to prevent that. My idea is to extend login verification, but check the existance of email address. Do you know any web services (prefereably WCF) that could do that?</p>