2.2.4.10.2 PidTagRecipientTrackStatus Property
Type: PtypInteger32 ([MS-OXCDATA] section 2.11.1)
The value of the PidTagRecipientTrackStatus property ([MS-OXPROPS] section 2.908) indicates the response status that is returned by the attendee. If this value is not set, it is assumed to be "respNone" (0x00000000). If set, it MUST be one of the following, as specified in section 2.2.1.11:
respNone
respAccepted (0x00000003)
respDeclined (0x00000004)
respTentative (0x00000002)