Want not to receive QoS 1 and 2 messages via MQTT while offline
The best practice for MQTT says, that QoS 1 and 2 messages are being held for an consumer even when/if currently not available, but sometimes it is not possible to reliable ensure, that waiting messages could be processed or even tranfered in the needed time.
With using QoS 1 and 2 in a message the sender correctly marks a message to be delivered to the appropriate client (at least once or exactly once).
But - like said - it is sometimes not possible to ensure that the given client will be able to process waiting messages without bringing the client into a threat.
To face this, a new configuration setting has been added, where it is possible to declare for a client, if QoS 1 and 2 messages are being held while offline (for the MQTT server).