Build a Scalable Email Notification System using Google Pub/Sub & Brevo (Node.js + Express)

📖 Introduction

In modern web applications, sending transactional emails — like welcome emails, password resets, or notifications — is a core feature. But sending 100s or 1000s of emails reliably, quickly, and without blocking the main server thread?

That’s a challenge.

In this Article, we’ll walk through how to build a production-ready email system using:

✅ Google Cloud Pub/Sub for queuing
✅ Brevo (Sendinblue) for email delivery
✅ Node.js with Express.js as the API
✅ Modular, scalable architecture ready for the real world

No prior GCP experience required. Beginner-friendly setup — explained step by step.

🧠 What You’ll Learn

• How to decouple email sending using queues

• How to use Google Cloud Pub/Sub in Node.js

• How to send dynamic transactional emails via Brevo

• A full working architecture you can test locally or deploy to production

🗂️ Project Architecture Overview

Here’s how the system works:

User/API triggers email ➝ Node.js (Express API) ➝ Publishes messages ➝ Google Cloud Pub/Sub ➝ Subscriber (Node.js Worker) ➝ Brevo ➝ Email sent

Let’s visualize it:

📦 Diagram (System Flow)

graph LR
A[Frontend/API] --> B[Express Server Producer]
B --> C[Google Pub/Sub Topic]
C --> D[Subscriber Service]
D --> E[Brevo API]
E --> F[User's Inbox]

🛠️ Tools & Technologies

⚙️ Step-by-Step Setup

📂 GitHub Repository

To make things easy for developers, the entire setup and step-by-step guide is available in the GitHub repo:

👉 GitHub: https://github.com/Vivek-018/email-service.git

Features included:

✅ Modular folder structure ✅ Working REST API route to send bulk emails
✅ Google Cloud Pub/Sub integration
✅ Brevo API connection using dynamic templates ✅ Secure environment config ✅ Ready to run locally or deploy to production

🧪 Local Demo

Once cloned, you’ll be able to:

• Start a Node.js server

• Publish email messages to Pub/Sub

• Automatically send real emails using Brevo to test accounts

All you need is:

• A Brevo account

• A Google Cloud project with Pub/Sub enabled

• Node.js installed locally

Full setup instructions are in the README.

🔁 End-to-End Email Flow

• You call POST /api/send-bulk-email with a list of users.

• The Express server publishes email jobs to Google Cloud Pub/Sub.

• The subscriber service listens to the topic, processes messages one-by-one.

• Each message triggers an email via Brevo.

• User receives a personalized email in their inbox.

🚀 Why This is Scalable

• Pub/Sub decouples producer & consumer — the API never waits for email delivery

• Pub/Sub automatically retries failed messages

• Multiple subscribers can run in parallel to handle large volumes

• Brevo handles email limits, spam compliance, delivery optimization

💡 Production Tips

• Add retry/backoff logic on the subscriber

• Use dead-letter topics for failed email jobs

• Use monitoring tools like Google Cloud Logging

• Deploy subscriber as a background worker or Cloud Run service

📂 Source Code

You can find the complete working setup on GitHub:

👉 GitHub Repository: https://github.com/Vivek-018/email-service.git

✅ Conclusion

By combining Google Pub/Sub with Brevo, you've built a reliable and scalable system that can send thousands of emails efficiently — without blocking your app or overloading your email provider.

This architecture is perfect for onboarding emails, alerts, reminders, receipts, and more.

Now go scale your communication like a pro!

Need Help?

Drop your questions below or open an issue in the GitHub repo!