Designing notifications for 100M users

- A staff‑level design thread laid out an architecture for notifications at 100 million users, detailing idempotency, priority queues, retry strategies, observability and tradeoffs across email, SMS and push channels. - The thread emphasised strict idempotency handling, priority‑ordered queues, backoff retry policies, and comprehensive metrics, and observability for debugging to compare latency/cost tradeoffs across channels. - It presents concrete trade‑offs and failure modes that differentiate senior designs from textbook answers, useful for staff‑level system design discussions. (x.com)