title: 422 or 409 status code for existing email during signup
body: <p>I am building RESTful API and I have come across a situation. During user sign up, if the email already exists then between <code>422</code> and <code>409</code> which http response code makes sense?<br><br>
  I have browsed through similar <a href="https://stackoverflow.com/questions/9269040/which-http-response-code-for-this-email-is-already-registered">one</a> and the accepted answer is from the year 2012. Does the answer still hold good? Examples would be of great help.</p>