How to Build a Reliable SMS Alert System for Marketplace Order Notifications

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A developer evaluation of SMS notification architecture for marketplace sellers recommends treating SMS as a secondary or urgent channel, with the application owning safety policies rather than the provider. The design writes an alert record before sending, uses idempotency keys to prevent duplicate messages, and polls delivery status until a final state is confirmed. Policy checks covering country allowlists, consent records, quiet hours, and spend thresholds must run before any SMS API call is made, since these guardrails are not managed by the provider. A per-user cooldown layer is also essential to prevent bursts of order updates from triggering accidental spam. The author provides a compact Python implementation demonstrating the full flow, including exponential backoff on rate-limit responses, which can be adapted to other languages like Node.js.

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