I started with the happy path and kind of assumed reliable delivery, which was a mistake.
Start by clarifying requirements and constraints, then design a scalable, reliable email service that integrates with the checkout flow. Focus on asynchronous processing, fault tolerance, and idempotency to handle high volume and ensure delivery.
Pro tip: Emphasize the importance of idempotency and exactly-once delivery semantics to avoid duplicate emails, and discuss how to handle failures with retries and dead-letter queues. Also, mention the need for monitoring and alerting on email delivery metrics.
Ask about scale (emails per second), latency requirements, delivery guarantees, and integration points with existing systems. Confirm whether emails are transactional and need to be sent immediately.
Outline the main components: an API endpoint to receive email requests from checkout, a message queue for asynchronous processing, a worker service to render and send emails, and a database for tracking status. Consider using a third-party email service like SES.
Discuss how to ensure reliability: idempotent email sending using unique order IDs, retry mechanisms with exponential backoff, and dead-letter queues for failed attempts. Explain how to scale workers horizontally and handle spikes.
Talk about trade-offs between synchronous vs asynchronous sending, using a third-party service vs building in-house, and how to handle email template updates. Consider edge cases like invalid email addresses, bounced emails, and user preferences.
Describe how to monitor the system: track email send rates, success/failure rates, latency, and queue depth. Set up alerts for anomalies and ensure logs are available for debugging.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.