public function validate()
    {
        if (count($this->_to) == 0
            && count($this->_cc) == 0
            && count($this->_bcc) == 0
        ) {
            return new SimpleEmailServiceError('Destination');
        }

        if (strlen($this->_source) == 0) {
            return new SimpleEmailServiceError('EmailSource');
        }

        if (strlen($this->_subject) == 0) {
            return new SimpleEmailServiceError('EmailSubject');
        }

        if (strlen($this->_body) == 0) {
            return new SimpleEmailServiceError('EmailBody');
        }
        return true;
    }