我把身体做成这样：

$params = [
  "personalizations" => [
    [
      "to" => [
        ["email" => "[email protected]"]
      ],
      "subject" => "testing subject for mail"
    ]
  ],
  "from" => [
    "email" => "[email protected]",
    "name" => $from_name
  ],
  "content" => [
    [
      "type" => "text/html",
      "value" => $message
    ]
  ],
  "headers" => [
    "Message-ID" => "<253618-testing-header>"
  ]
];

然后像这样发送：

$request =  $url . 'api/mail.send.json';
$cr = curl_init($request);
curl_setopt($cr, CURLOPT_POSTFIELDS, json_encode($params));
curl_setopt($cr, CURLOPT_POST, true);
curl_setopt($cr, CURLOPT_HTTPHEADER, array("Authorization: Bearer test"));
curl_setopt($cr, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($cr);
$out = json_decode($response, true);

但它显示空从电子邮件地址（必需的）。
通常我们是这样使用params的：

$params = array(
'to'        => $to,
'subject'   => $subject,
'html'      => $message,
'from'      => $from,
'fromname'  => $from_name,
);

但现在我想设置消息ID头，所以有人建议前面提到的方式。
有人能帮帮忙吗？