I want to be able to use MAPIFolder.Items.Restrict() to return me a
collection of items that my program has not yet processed. After I
process items, I mark them w/ a custom string UserProperty that I set
to a GUID.

"If you are trying to use the Find or Restrict methods with
user-defined fields, the fields must be defined in the folder,
otherwise an error will occur."-MSDN
(http://msdn.microsoft.com/library/de...HV05247704.asp)

What is the proper way to add my UserProperty to the MAPIFolder such
that I can use the Restrict method to return me the results I'm looking
for?

What query string should I pass to Restrict() that would get me all
Items that are not marked w/ my string GUID?

Thanks!
Jeff