How to select any message in folder

[s0muel]

So ... I`m trying to replace e-mail item attachments. For this I`m adding new mail item and deleting old one. Can I select new e-mail item and if I can, how to do it...
I know that exist a list if selected mail items what I can get for example in such way:

pIGWClientState->get_SelectedMessages(&pIDisp);
if (pIDisp){
pIDisp->QueryInterface(IID_IGWMessageList, (void**)&pIMessageList);
pIDisp.Release();
if (pIMessageList) {
long lCount;
pIMessageList->get_Count(&lCount);
for (int i= 0; i < lCount; i++) {
pIMessageList->Remove(CComVariant(i));
}

also there exists a method like add:
pIMessageList->Add(CComVariant( ? ))
I`m tried use mail ID but I`m not succeeded
but I`m not find any document with description this method
from header file:
STDMETHOD(Add)(THIS_ VARIANT Message) PURE;
what I do wrong.
Does anybody knows decision?
Thank You.