Nodemailer
If you have a need to send email from your Node.js application, there is a good chance you will end up doing it with Nodemailer.
In the early days of the JavaScript-on-the-server ecosystem, Andris Reinman started the Nodemailer project. He has maintained it since 2010, and it has a reputation for being a rock-solid standard.
Your average JavaScript project (this website included!) is composed of thousands of small open-source packages - a complex pyramid of dependencies that build upon one another. Not so for Nodemailer!
Nodemailer has no dependencies. It runs on everything from Node v6 forward. It is security-focused. It is too good for the JavaScript world and we do not deserve it.