New events have been added to the Microsoft Outlook object model that let your program detect when attachments have been added to or opened in an item and when an attempt is being made to change an existing attachment.
All items that support attachments now fire the AttachmentAdd event when an attachment is added to the item. When a user opens an attachment in an item, the item fires the AttachmentRead event. If the user attempts to save an open attachment, the item fires the BeforeAttachmentSave event; the event handler can cancel the default action for this event, preventing the user from changing the attachment.