2.2.3.2.14 Suppression of Automatic Replies
To set the value of the PidTagAutoResponseSuppress property (section 2.1.3.2.20) to -1, indicating that all automatic replies to the message are to be suppressed, clients SHOULD write an X-Auto-Response-Suppress header with the value "All". Clients MAY, instead, write a Precedence header (2) with any value.
To set the value of the PidTagAutoResponseSuppress property to a more specific value, clients write an X-Auto-Response-Suppress header with one or more values selected from the table in section 2.1.3.2.20.
MIME readers SHOULD<116> map individual elements of an X-Auto-Response-Suppress header to bits in the value of the PidTagAutoResponseSuppress property according to the table. If both the X-Auto-Response-Suppress and Precedence headers are present, the PidTagAutoResponseSuppress property value SHOULD be 0xFFFFFFFF but MAY<117> be 0x00000000. If the value of the X-Auto-Response-Suppress header is other than as specified in the table in section 2.1.3.2.20, MIME readers SHOULD<118> ignore the entire header.