This change is intended to address a behavior of the router that might be considered misleading.
When messages are delivered to an address that has a multicast distribution, delivery disposition and settlement cannot be tracked because there may be multiple consumers. Because of this, if a delivery is unsettled, the first router will settle the message unilaterally and forward it on in a pre-settled state. The result is that the sender may receive a settled-and-accepted disposition for a message that was eventually dropped without being delivered to a consumer.
The solution is to reject deliveries to multicast addresses that are not already pre-settled by the sender. The rejection shall carry the text: "Deliveries to a multicast address must be pre-settled".
This behavior shall be the new default behavior. A configuration flag shall be provided to restore the original behavior.