code: function(email) {
                  console.log('iamInterface.email.availability', email);
                  corbel.validate.value('email', email);
  
                  return this.request({
                      url: this._buildUriWithDomain(this.uri, email),
                      method: corbel.request.method.HEAD
                  }).then(
                      function() {
                          return false;
                      },
                      function(response) {
                          if (response.status === 404) {
                              return true;
                          } else {
                              return Promise.reject(response);
                          }
                      }
                  );
              }
docs: Return availability endpoint.
  @method
  @memberOf corbel.Iam.EmailBuilder
  @param  {String} email The email.
  @return {Promise}     A promise which resolves into email availability boolean state.