How to: Access a Message on an IMAP Store Without Downloading the Entire Message

This topic shows a code sample in C++ that queries a message store for the IProxyStoreObject interface, and uses the returned pointer and the IProxyStoreObject::UnwrapNoRef function to obtain a pointer to an IMAP store object that has been unwrapped. Using this unwrapped store allows access to a message in its current state without invoking a download of the entire message.

Because UnwrapNoRef does not increment the reference count for this new pointer to the unwrapped store object, after successfully calling UnwrapNoRef, you must call IUnknown::AddRef to maintain the reference count.

  HRESULT HrUnWrapMDB(LPMDB lpMDBIn, LPMDB* lppMDBOut)
{
    HRESULT hRes = S_OK;
    IProxyStoreObject* lpProxyObj = NULL;
    LPMDB lpUnwrappedMDB = NULL;
    hRes = lpMDBIn->QueryInterface(IID_IProxyStoreObject,(void**)&lpProxyObj);
    if (SUCCEEDED(hRes) && lpProxyObj)
    {
        hRes = lpProxyObj->UnwrapNoRef((LPVOID*)&lpUnwrappedMDB);
        if (SUCCEEDED(hRes) && lpUnwrappedMDB)
        {
            // UnwrapNoRef doesn't addref, so do it here
            lpUnwrappedMDB->AddRef();
            (*lppMDBOut) = lpUnwrappedMDB;
        }
    }
    if (lpProxyObj) lpProxyObj->Release();
    return hRes;
}