The IMAPISession::QueryDefaultMessageOpt method retrieves the message option properties for a particular address type.
HRESULT QueryDefaultMessageOpt(
LPTSTR lpszAdrType,
ULONG ulFlags,
ULONG FAR * lpcValues,
LPSPropValue FAR * lppOptions
);
The IMAPISession::QueryDefaultMessageOpt method retrieves the one or more message option properties that a transport provider supports for the address type pointed to by the lpszAdrType parameter. Message option properties control a message's behavior after it is submitted to the transport provider; they are part of the message envelope, not its content.
The property value array pointed to by lppOptions includes the property tags and values for each of the message option properties.