Exchange EWS API - Assign and check if appointment has Extended Property

Hi All,

I'm working on integrating our Exchange server with our Intranet calendar. I'm trying to pass a GUID from my database to the Exchange appointment via Extended Properties. It's working fine if I filter the view but I need a way of iterating through all appointments within a specific date range and checking if they've got the property attached.

This is my code so far:

service.UseDefaultCredentials = True
        service.Url = New Uri("https://mail.server.com/ews/exchange.asmx")

        Using db As New DBDataContext
            'Grab events from Portal DB
            Dim MyCalendar = (From c In db.crm_Calendars Where c._Staff_ID = New Guid("BB12A5EB-1E99-47AD-BA0D-B727FDA47C5B") And c.Type = CalendarType.Personal).FirstOrDefault

            ' Check with Exchange
            Dim startDate As DateTime = DateTime.Now
            Dim endDate As DateTime = DateTime.Now.AddDays(3)
            Const NUM_APPTS As Integer = 5

            Dim calendar As CalendarFolder = CalendarFolder.Bind(service, WellKnownFolderName.Calendar, New PropertySet())
            Dim cView As New CalendarView(startDate, endDate, NUM_APPTS)
            cView.PropertySet = New PropertySet(AppointmentSchema.Subject, AppointmentSchema.Start, AppointmentSchema.End)
            Dim appointments As FindItemsResults(Of Appointment) = calendar.FindAppointments(cView)
            For Each a In appointments

Dim def As New ExtendedPropertyDefinition(DefaultExtendedPropertySet.PublicStrings, "AppointmenId", MapiPropertyType.[Strin