Arbitrary MIME Headers

To generate an arbitrary header on a MIME message, a client creates a named property in the PS_INTERNET_HEADERS property set, with the property name equal to the header name and the data type equal to the PtypString data type ([MS-OXCDATA] section 2.11.1). The value of this property is set to the MIME header value.

MIME writers use the name and value of such a property to create a header on the generated MIME message with the corresponding name and value. MIME writers encode the header value as specified in [RFC2047], according to the conditions specified in section 1 of that document.<33> MIME writers MUST NOT create such a header if a different Message object property is already mapped to the same header (2). MIME writers SHOULD NOT<34> create such a header if the header name begins with one of the reserved name prefixes "X-Microsoft-Exchange-Organization" or "X-Microsoft-Exchange-Forest".