邮件的 content 为空，但 html 字段有值

接口返回数据如下：

```json
 "message": {
        "id": "",
        "from_address": "",
        "to_address": null,
        "subject": "验证码",
        "content": "",
        "html": "您的邮箱验证码是 效期 5 分钟\n",
        "received_at": 1762250200602,
        "sent_at": 1762250200602,
        "type": "received"
    }
```

请问这个是邮件发送方的问题吗？