89c0777d_HiveMQ_1_4_1___User_Guide_Table_3__Static_properties_Description
[Property Name] messages.maxInflight [Default Value] 20 [Description] 
The maximum number of QoS 1 or 2 messages that can be in the process of being transmitted simultaneously. This includes messages currently going through handshakes and messages that are being retried. Set to 0 for no maximum. If set to 1, this will guarantee in-order delivery of messages for QoS1 und QoS2.
HiveMQ 1.4.1 - User Guide
Description