Timeout with Nodemailer and Firebase

A few days ago, I was trying to use Nodemailer in Firebase with a configuration such as:

jsx
const mailTransport = nodemailer.createTransport({
    
    host: 'auth.mail.pro',
    port: '25',
    auth: {
        user: 'user@user.com',
        pass: 'securePassword'
    }
    
});

The problem was that I was getting a timeout error. The port 25 caused the issue; Google Cloud Functions blocks this port by default for security reasons.

It seems that this port was the most used by spammers.

The solution was to use port 587 or port 465.