I’ve followed the Postfix , Ubuntu tutorial for setting up Postfix as a send only SMTP server on a droplet. The implementation of Postfix works fine and passed the tests found on the tutorial. Now how can I connect a backend like Node.js to Postfix so I can collect form submitted data and email them through Postfix? Thank you.

https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-as-a-send-only-smtp-server-on-ubuntu-16-04