2.2.3.2.16 Message Flagging
To set the value of the PidLidFlagRequest property ([MS-OXCSPAM] section 2.2.1.3), clients MUST write the value to an X-Message-Flag header.
MIME readers copy the value of an X-Message-Flag header to the value of the PidLidFlagRequest property. In addition, when an X-Message-Flag header is present, MIME readers SHOULD<122> do all the following:
Set the value of the PidTagFlagStatus property ([MS-OXOFLAG] section 2.2.1.1) to 2 (denoting that the message is flagged).
Copy the value of the PidTagSubject property ([MS-OXPROPS] section 2.1034) to the value of the PidLidToDoTitle property ([MS-OXOFLAG] section 2.2.1.12).
Set the value of the PidLidTaskStatus property ([MS-OXOTASK] section 2.2.2.2.2) to 0 (zero) (denoting that a task is not started).
Delete or disregard any existing property values for the following properties:
Set the value of the PidLidTaskComplete property ([MS-OXOTASK] section 2.2.2.2.20) to FALSE.
Set the value of the PidLidPercentComplete property ([MS-OXOFLAG] section 2.2.2.3) to 0.0.
Set the value of the PidTagToDoItemFlags property ([MS-OXPROPS] section 2.1049) to 8.