Node.js SMTP & MongoDB Gateway

I’m building a dedicated SMTP gateway in Node.js that will handle our application’s transactional emails end-to-end. All outgoing messages should be queued in MongoDB, processed asynchronously, and sent through a robust SMTP layer with standard AUTH methods.

The core features I need are:
• Email queuing to smooth traffic bursts and enable throttling
• Automatic bounce handling that records hard/soft bounces back into MongoDB
• Effective spam filtering, preferably by integrating a proven engine such as SpamAssassin or an equivalent Node module

You’re free to leverage frameworks like Haraka, Nodemailer, or craft a custom solution—whichever lets us reach solid throughput, clean logs, and straightforward maintenance.

Deliverables will include the full source in a Git repo, a Dockerfile or bash script for one-command deployment on Ubuntu, the MongoDB schema, and quick-start documentation that proves the system can send a 10 000-message test batch while capturing bounces accurately.

When you reply, focus on your relevant experience designing or maintaining similar email infrastructures, especially any work with queueing, bounce parsing, and spam mitigation at scale. I’m ready to spin up a fresh VPS as soon as the design is set, so let me know how you’d tackle it and any libraries you prefer.