Folder Extended Properties (EWS+Outlook)

Question

What Im trying to achive is to be able to create a Folder with Extended Properties using EWS and then be able to read these properties from inside Outlook.
Ive verified that it works to add & retrieve extended properties on Folders using EWS, i.e.
        var f = new Folder(_svc);
f.DisplayName = "Testing";
        f.SetExtendedProperty(EPD.ItqAction, 1);
        f.Save(WellKnownFolderName.MsgFolderRoot);
then loading it as following,
        PropertySet propset = new PropertySet(PropertySet.IdOnly);
        propset.Add(EPD.ItqAction);
        f.Load(propset);
or even using SearchFilder.IsEqual()
but these Properties does not appear in OutlookSpy nor MFCAPI, and can't seem to be accessable from Outlook VSTO.
I've tried 
myFolder.PropertyAccessor.GetProperty(EPD.ItAction.ToMapiString());
ToMapiString creates a "http://schemas.microsoft.com/mapi/{GUID}/attr-name" string
But this results in a COMException. 
Ive heard that named Properties are not supported by Outlook, what is the alternative type definition? And that one should create a Hidden Item in the folder for properties. But haven't been able to find any details on how to create a hidden item (only Hidden
folders w/ attribute 0x10f4).

Answer 1

>user defined properties are vanished if they are not defined in the delivery store".
What exactly do you mean? How is that possible?
>I'd recommend asking EWS specific questions on the Exchange dev forums instead
Eugene, I am answering this question in the Outlook dev forum. It is perfectly fine here. If you do not know how to answer it, you do not have to reply. There is no requirement that you answer each and every question asked in the forum.
Dmitry Streblechenko (MVP)
http://www.dimastr.com/redemption
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