How to Prevent Duplicate Notifications in Node.js Bulk Email and SMS Systems

Developers building bulk notification systems in Node.js face a core challenge: ensuring messages are sent exactly once across email, SMS, queues, and scheduled pollers. The recommended approach involves writing each notification intent to a durable outbox table within the same database transaction as the triggering business event, keeping the two concerns cleanly separated. A queue worker then claims small batches of outbox rows using leases, allowing other workers to recover tasks if a process dies mid-delivery. Every delivery attempt must be idempotent, with a stable deduplication key per channel, since true exactly-once delivery cannot be guaranteed across distributed systems. Email and SMS workloads should maintain separate concurrency budgets to prevent one channel's retries or slowdowns from starving the other.