Delivery reports

A provider HTTP 200 means the message was accepted for submit, not delivered. Terminal states come from delivery reports (or the simulated DLR scheduler).

GET /v1/messages/:id to poll. Subscribe to message.delivered / message.failed / message.expired / message.rejected for push.

+233200000005 delivers after a delay. +233200000006 times out and is UNSAFE_TO_RETRY — Taysend will not failover that attempt.