2.2.1 DRS_MSG
The data carried by the MAIL_REP_MSG_V1 or MAIL_REP_MSG_V2 message MUST be a Network Data Representation (NDR)–encoded binary large object (BLOB) that contains one of the following DRS Remote Protocol structures, as specified in [MS-DRSR]:
DRS_MSG_GETCHGREQ_V4
DRS_MSG_GETCHGREQ_V7
DRS_MSG_GETCHGREPLY_V1
DRS_MSG_GETCHGREPLY_V6
The dwMsgVersion field of the MAIL_REP_MSG_V1 or MAIL_REP_MSG_V2 message identifies whether the payload is a DRS request message or a DRS response message and indicates the version of the DRS request or response.
Other DRS message structures MUST NOT be carried as payload of the DRS Protocol Extensions for SMTP.