Build a Rate Limiter With Delivery Tracking

Problem Build a per-account rate limiter for an outbound messaging API: each account may send at most a fixed rate (e.g. 5 messages/second), and sends beyond that are throttled or queued. Alongside the limiter, track the delivery status of every message as it moves through queued → sent → delivered/failed.

Input / Output

• Input: send requests keyed by account id, arriving concurrently over time.
• Output: an accept/throttle decision per send, plus the current status of any message.

Constraints

• Many accounts, each with an independent limit.
• Concurrent sends to the same account must not exceed the limit.

Example

• Limit 5 msg/sec/account; the 6th message in the same second is throttled or queued.