In the case where the broker is used as part of a public service, the service provider may not be able to control consumer client code, and need some mechanism to enforce consumers that never ack a message to not hold up that message in the broker.

Having a configurable address-setting for configuring a consumer ack timeout would be helpful for this use case.

The AMQP also accepts this as a possible behavior by the broker:

The source MAY spontaneously attain the modified outcome for a message (for example the source might implement some sort of time-bound acquisition lock, after which the acquisition of a message at a node is revoked to allow for delivery to an alternative consumer with the message modified in some way to denote the previous failed, e.g., with delivery-failed set to true).