sender.js

const nodemailer = require("nodemailer");
const fs = require("fs");

const readFile = (path, opts = "utf8") => {
  return new Promise((resolve, reject) => {
    fs.readFile(path, opts, (err, data) => {
      if (err) reject(err);
      else resolve(data);
    });
  });
};

async function main() {
  // Generate test SMTP service account from ethereal.email
  // Only needed if you don't have a real mail account for testing
  let html = await readFile("index.html");

  // create reusable transporter object using the default SMTP transport
  var transport = nodemailer.createTransport({
    host: process.env.SMTP,
    port: Number(process.env.PORT),
    secure: false, // upgrade later with STARTTLS
    auth: {
      user: process.env.USER,
      pass: process.env.PASSWORD
    }
  });

  // send mail with defined transport object
  let info = await transport.sendMail({
    from: '"Fred Foo 👻" <fulano@email.com>', // sender address
    to: "bc48cdd21b-0e7d4f@inbox.mailtrap.io", // mailtrap email
    subject: "Hello ✔", // Subject line
    text: "Hello world?", // plain text body
    html: html, // html body
  });

  console.log("Message sent: %s", info.messageId);
  // Message sent: <b658f8ca-6296-ccf4-8306-87d57a0b4321@example.com>

  // Preview only available when sending through an Ethereal account
  console.log("Preview URL: %s", nodemailer.getTestMessageUrl(info));
  // Preview URL: https://ethereal.email/message/WaQKMgKddxQDoou...
}

main().catch(console.error);