Nodemailer is a mailer for nodejs and it is very easy to use.
The libraries:
pnpm install nodemailer dotenv
The code:
require("dotenv").config();
const nodemailer = require('nodemailer');
const transporter = nodemailer.createTransport({
    host: process.env.MAIL_SERVER,
    port: process.env.MAIL_PORT,
    secure: true,
    auth: {
        user: process.env.ADMIN_EMAIL,
        pass: process.env.ADMIN_PASSWORD
    },
});
async function mailBook(book) {
    const message = {
        from: process.env.ADMIN_EMAIL,
        to: "hi@example.com",
        subject: 'Subject',
        html: "Body.",
    };
    return await transporter.sendMail(message);
}
I use dotenv to load in the .env file which contains the mailing information. You could also hardcode these in but then accidentally uploading to github becomes a danger.