MQTTnet.Extensions.ManagedClient Then this is _null_ the message was processed successfully without any error. This is null when the connection was failing and the server was not reachable. The subscriptions are managed in 2 separate buckets: and are processed during normal operation and are moved to the when they get processed. They can be accessed by any thread and are therefore mutex'ed. get sent to the broker at reconnect and are solely owned by . Defines the maximum amount of topic filters which will be sent in a SUBSCRIBE/UNSUBSCRIBE packet. Amazon Web Services (AWS) limits this number to 8. The default is int.MaxValue.