protected function initializeSoapClient()
    {
        $this->soap = new SoapClient(
            dirname(__FILE__) . '/assets/services.wsdl',
            array(
                'user' => $this->username,
                'password' => $this->password,
                'location' => 'https://' . $this->server . '/EWS/Exchange.asmx',
                'classmap' => $this->classMap(),
                'curlopts' => $this->curl_options,
                'features' => SOAP_SINGLE_ELEMENT_ARRAYS,
            )
        );

        return $this->soap;
    }