gistfile1.txt

var data = JSON.stringify({
  "personalizations": [
    {
      "to": [
        {
          "email": "joseeduardobarros@gmail.com"
        }
      ],
      "subject": "Hello, World!"
    }
  ],
  "from": {
    "email": "mailman@elbit.com.br"
  },
  "content": [
    {
      "type": "text",
      "value": "Olá, mundo"
    }
  ]
});

var xhr = new XMLHttpRequest();
xhr.withCredentials = true;

xhr.addEventListener("readystatechange", function () {
  if (this.readyState === 4) {
    console.log(this.responseText);
  }
});

xhr.open("POST", "https://api.sendgrid.com/v3/mail/send");
xhr.setRequestHeader("authorization", "Bearer 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");
xhr.setRequestHeader("content-type", "application/json");
xhr.setRequestHeader("cache-control", "no-cache");
xhr.setRequestHeader("postman-token", "3acd8f0c-b544-b8b1-5507-79737757243e");

xhr.send(data);