27.2. WOrking with Item-Level Events
In addition to the application-level events discussed so far, Outlook also supports a wide variety of item-level events — events that fire when items are manipulated rather than the application as a whole being affected.
You can handle item-level events in Outlook in two ways:
By declaring an event in a class module and running an initialization procedure, so that VBA then traps the event when it fires. This chapter takes this approach.
By creating Visual Basic Script (VBScript) code and placing it in the form used by the item. This approach is especially useful for custom forms, but it is more limited than the previous approach, because some of the events that Outlook supports are not available in VBScript. ...