The IResponse::AddHeader method adds an HTTP header to the HTTP response. For more information, see the AddHeader method of the Response object.
HRESULT AddHeader(
BSTR bstrHeaderName, //a binary string that contains the name of
// the HTTP header
BSTR bstrHeaderValue //a binary string that contains the header
// value
);
This method adds an HTTP header with a specified value; it also always adds a new HTTP header to the response. It will not replace an existing header of the same name. Once a header has been added, it cannot be removed.