The unique Id of the message.
This property defines the unique Id of the message. When sending files the class will automatically generate a value in the format "GUID@nsoftware". When receiving files the Id will be populated with the value read from the message.
In most cases there is no need to set this value, however if a file needs to be retransmitted using the same message Id for reliability this may be set. In AS4Client this may be set before calling SendFiles. In AS4Server this may be set after calling ReadRequest and before calling SendResponse.
This property is not available at design time.