# Operate messaging reliably

Diagnose failures, handle retries, and keep your customers’ preferences at the centre.

## The delivery incident

The morning delivery report has changed. Resolve a bounce, prevent duplicate processing, and restore a reliable notification workflow.

1. Diagnose the bounce
2. Handle a retry
3. Verify the sender
4. Resolve event ordering
5. Respect a preference
6. Independent challenge

Exercises are in English. Progress saves to your Bird account. All messages are simulated. The final assessment requires all six checks and pauses course hints.

[Open the practice workspace](/learn/lab/reliability)