Customer.io Rate Limits

Prerequisites

• Current provider limit documentation/plan, a measured baseline, idempotency design, and a named capacity owner.
• Synthetic test payloads and alerting for 429s, queue age, delivery failure, and duplicate-event risk.

Output

• A rate-aware client/workflow configuration with bounded concurrency, backoff, idempotency, monitoring, and a safe replay decision path.
• An aggregate load-test or incident receipt showing limit behavior without recipient payloads.

Examples

Send synthetic events at gradually increasing concurrency below the approved limit, record 429s and queue age, and apply exponential backoff with jitter using a stable idempotency key. If throttling occurs, reduce concurrency and allow recovery; do not retry every failed event immediately or widen sends to compensate.

Overview

Understand Customer.io's API rate limits and implement proper throttling: token bucket limiters, exponential backoff with jitter, queue-based processing, and 429 response handling.