The aPropID structure is an array used to specify queue, message, and machine property identifiers. It is used to identify which properties are specified for a call. MSMQ uses three different types of property identifiers: QUEUEPROPID, MSGPROPID, and QMPROPID.
typedef PROPID MSGPROPID
typedef PROPID QUEUEPROPID
typedef PROPID QMPROPID