Private WithEvents ConfirmAppointment As Office.CommandBarButton

Private Sub Application_ItemContextMenuDisplay(ByVal CommandBar As Office.CommandBar, _
  ByVal Selection As Selection)
  Dim obj As Object
  Dim Item As Outlook.AppointmentItem
  Dim Btn As Office.CommandBarButton
  Dim Caption$

    ' Edit
  Caption = "Confirm Appointment"

  If Selection.Count = 1 Then
    Set obj = Selection(1)
    If TypeOf obj Is Outlook.AppointmentItem Then
      Set Item = obj
      Set Btn = CommandBar.Controls.Add(msoControlButton, , , , True)
      Btn.Style = msoButtonCaption
      Btn.Caption = Caption
      Btn.Parameter = Item.EntryID
      Set ConfirmAppointment = Btn
    End If
  End If
End Sub

Private Sub ConfirmAppointment_Click(ByVal Ctrl As Office.CommandBarButton, _
  CancelDefault As Boolean)
  Dim Appt As Outlook.AppointmentItem
  Dim Mail As Outlook.MailItem
  Dim Link As Outlook.Link
  Dim Contact As Outlook.ContactItem
  Dim Message$, StartTime$, Recipient$, Subject$
  Dim EntryID$

  EntryID = Ctrl.Parameter
  If Len(EntryID) Then
    Set Appt = Application.Session.GetItemFromID(EntryID)
  End If

  If Not Appt Is Nothing Then
    Set Mail = Application.CreateItem(olMailItem)

    If Appt.Links.Count Then
      Set Link = Appt.Links(1)
      If Not Link.Item Is Nothing Then
        Set Contact = Link.Item
        If Not Contact Is Nothing Then
          Recipient = Contact.Email1Address
        End If
      End If
    End If

    ' Edit
    Subject = "Confirmation: " & Appt.Subject
    Message = "Herewith I confirm the following appointment: "

    StartTime = Format(Appt.Start, "dddd, dd. mmm yyyy hh:nn", vbUseSystemDayOfWeek, vbFirstFourDays)
    Message = Message & vbCrLf & StartTime

    Mail.To = Recipient
    Mail.Subject = Subject
    Mail.Display
    Mail.Body = Message & Mail.Body
  End If

  Set ConfirmAppointment = Nothing
End Sub