What is Nodemailer, and how does it let a Node.js application send emails via SMTP?

Nodemailer is the most widely used Node.js library for sending email, supporting SMTP (talking directly to a mail server or provider like Gmail, SendGrid, or Amazon SES over the standard email protocol) as well as several transport methods -- it handles the details of MIME message formatting, attachments, and HTML/plain-text bodies behind a simple, promise-based API.

const nodemailer = require('nodemailer');

const transporter = nodemailer.createTransport({
  host: 'smtp.sendgrid.net',
  port: 587,
  auth: { user: 'apikey', pass: process.env.SENDGRID_API_KEY },
});

await transporter.sendMail({
  from: 'noreply@example.com',
  to: user.email,
  subject: 'Welcome!',
  html: '<h1>Welcome to our platform</h1>',
});