Design a Notification System: A Complete System Design Guide | by Madhur Banger | Medium
This guide outlines how to build a scalable notification service supporting email, SMS, push and in-app channels. It covers user preferences, rate-limiting, synchronous & batch delivery, queueing with retries, high availability, and trade-offs between latency, cost and reliability. Think about the apps you use every day. A banking app alerts you about suspicious activity. A shopping app lets you know when your order ships. A chat app pings you when a friend sends a message. All of these rely on a notification system working seamlessly behind the scenes. On the surface, notifications feel simple — you receive a message or alert, and that’s it. But under the hood, they’re surprisingly complex. Delivering millions of notifications across email, SMS, push, and in-app channels requires careful planning, robust infrastructure, and a design that can scale. That’s why learning how to design a notification system is so important. It’s not just a valuable System Design interview question — it’s