How to make subject field compulsory in Outlook 2007?

Private Sub Application_ItemSend(ByVal Item As Object, ByRef Cancel As Boolean)

  If Item.Subject = "" Then
    Item.Subject = InputBox("Please do not always forget the subject!")
  End If

  If Item.Subject = "" Then
    MsgBox "Won't send this without a subject."
    Cancel = True
  End If
End Sub

Do While Item.Subject = ""
Item.Subject = InputBox("..")
Loop