title: React unable to send email with SendGrid
body: <p>I am using react to send emails: </p>
  
  <pre><code>const sgMail = require('@sendgrid/mail');
  sgMail.setApiKey(process.env.REACT_APP_SENDGRID);
  const msg = {
    to: 'test@example.com',
    from: 'test@example.com',
    subject: 'Sending with SendGrid is Fun',
    text: 'and easy to do anywhere, even with Node.js',
    html: '&lt;strong&gt;and easy to do anywhere, even with Node.js&lt;/strong&gt;',
  };
  sgMail.send(msg);
  </code></pre>
  
  <p>But I got the following error:</p>
  
  <pre><code>Access to fetch at 'https://api.sendgrid.com/v3/mail/send' 
  from origin 'http://localhost:3000' has been blocked by CORS policy: 
  Response to preflight request doesn't pass access control check: 
  The 'Access-Control-Allow-Origin' header has a value 'https://sendgrid.api-docs.io' that is not equal to the supplied origin. 
  Have the server send the header with a valid value, or, if an opaque response serves your needs, 
  set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
  </code></pre>
  
  <p>How do I fix it? Many thanks!</p>