Get the ordered routes an alert to this recipient would walk

The ladder in the order delivery would try it: the first route that gets the alert out wins, the rest are fallbacks.

A route in this list is not a promise of delivery. Routes are built from the recipient's contacts; whether the transport behind the provider is actually up is a separate question, and it is answered per route by deliverable. A route with deliverable: false would be attempted and would fail — blocked_by carries the same machine-readable code the availability endpoint uses, and scope says who repairs it: recipient (missing or disabled contact) or installation (mailer, credentials, telephony). This is one verdict shared with GET /recipients/{recipient}/availability and with the status of GET /capabilities: if those two say a channel is not set up, the route over it reads deliverable: false here rather than looking healthy.