public function jsonSerialize()
    {
        return array_filter(
            [
                'bcc' => $this->getBccSettings(),
                'bypass_list_management' => $this->getBypassListManagement(),
                'footer' => $this->getFooter(),
                'sandbox_mode' => $this->getSandboxMode(),
                'spam_check' => $this->getSpamCheck()
            ],
            function ($value) {
                return $value !== null;
            }
        ) ?: null;
    }