Use the Sendgrid API

sendgrid.js

//Form.js
class Form extends React.Component {
  constructor() {
    super();
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleSubmit(event) {
    event.preventDefault();
    const data = new FormData(event.target);

    fetch('/api/form-submit-url', {
      method: 'POST',
      body: data,
    });
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label htmlFor="username">Enter username</label>
        <input id="username" name="username" type="text" />

        <label htmlFor="email">Enter your email</label>
        <input id="email" name="email" type="email" />

        <label htmlFor="birthdate">Enter your birth date</label>
        <input id="birthdate" name="birthdate" type="text" />

        <button>Send data!</button>
      </form>
    );
  }
}
//index.js

    const sgMail = require('@sendgrid/mail');
    sgMail.setApiKey(process.env.SENDGRID_API_KEY);
    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: '<strong>and easy to do anywhere, even with Node.js</strong>',
    };

sgMail.send(msg);