title: jQuery validate + AJAX e-mail availiability check
body: <p><strong>UPDATED</strong>
  I'm using jQuery validate plugin and remote method to check email availiability with ajax, but I don't understand why ajax calls only once. When email is entered ajax makes call and in console prints email that is entered, but if i delete it and write in another email nothing happens.</p>
  
  <p>HTML</p>
  
  <pre><code>&lt;input type="text" name="on0" value="Your e-mail" class="form-field no-mr check-email"&gt;
  </code></pre>
  
  <p>jQuery</p>
  
  <pre><code>jQuery.validator.addMethod('defaultInvalid', function(value, element) {
      return !(element.value == element.defaultValue);
  }, 'Custom Error Message for this field');
  
  $('.checkout-form').validate({
      rules: {
          on0 : 'required defaultInvalid email'
      }
  });
  
  $('.check-email').rules("add", {
      "remote" : {
          url: 'c/',
          type: "post",
          dataType: 'html',
          data: {
              check: function() {
                  return $('.check-email').val();
              }
          },
          success: function(data){
              console.log(data);
          },
          error: function(data){
              console.log(data);
          }
      }
  });
  </code></pre>
  
  <p>PHP where ajax makes post</p>
  
  <pre><code>&lt;?php 
  
  echo $_POST['check'];
  
   ?&gt;
  </code></pre>