System Design: Scalable Event Management and Email Notification Pipeline

Context

Design a production-ready system to manage events and notify all registered participants by email. The platform must support at least 1,000,000 events and scale horizontally. Assume multiple services, multi-tenant usage, and a mix of small and very large events.

Requirements

• Functional
  1. Create and update events.
  2. Register and unregister participants to events.
  3. Trigger notifications per event (e.g., event updates, reminders) and send emails to all registered participants.
  4. Respect unsubscribe preferences; handle bounces and complaints to maintain a suppression list.
• Non-functional
  1. Scale to ≥ 1,000,000 events and high fan-out notifications.
  2. High throughput email pipeline with batching, prioritization, rate limiting, and retries.
  3. Idempotency and deduplication across API, queue, and sender. Clear delivery semantics.
  4. Horizontal scaling, partitioning/sharding strategy.
  5. Strong observability, failure handling, disaster recovery, and cost awareness.

Deliverables

• APIs: create/update event, register/unregister participant, trigger/send notifications.
• Data models and storage choices.
• Email job enqueueing, batching, prioritization strategy.
• Scale assumptions and estimates: participants per event, peak QPS, daily email volume.
• Rate limiting and exponential backoff to meet provider quotas.
• Idempotency, deduplication, retry, bounce/complaint handling, unsubscribe preferences.
• Architecture: services, queues/streams, databases, caches, partitioning, horizontal scaling.
• Consistency requirements and delivery semantics (at-least-once vs exactly-once).
• Observability: metrics, tracing, alerting.
• Failure scenarios, disaster recovery, and cost considerations.