Custom DNS resolving with Nodemailer

transport.js

// The following example sets up Nodemailer in a way that it does not perform any DNS resolving on its own

const hostname = 'smtp.gmail.com';
const resolved = (await dns.promises.resolve(hostname))[0];

const transporter = nodemailer.createTransport({
    host: resolved, // <- IP address of the SMTP server
    name: 'my.machine.hostname', // <- PTR name of sender's public IP address, ends up in the Recieved: header
    tls: {
        servername: hostname, // <- hostname of the SMTP server, needed to verify TLS
        rejectUnauthorized: true, // <- allow only valid certs
        minVersion: 'TLSv1.2' // <- allow TLSv1.2+, this matches MTA-STS requirements
    },
    port: 465,
    secure: true,
    auth: {
        user: 'username',
        pass: 'secret'
    }
});