Have you register an Exchange 2000 store event sink globally on the mailbox store, the sink fires for the appropriate events (OnSyncSave, for example) for all folders in a mailbox. However, the sink does not fire for events in the Outbox or the Sent Items Folder?
For example, when a user sends an e-mail, it appears in the Outbox folder for a brief time.
Outbox: This is due to Even if an event sink is registered directly on the Outbox, it will not fire.
The Outbox is a temporary home for a new message while it waits to be picked up by the MAPI spooler. When the message appears in this folder, it does not generate an OnSave or OnSyncSave event. Also, when the message disappears from the folder, it does not generate an OnDelete or OnSyncDelete event.
Sent Items: Messages are moved to the Sent Items folder after being sent by the MAPI client in such a way that events are not generated, and this behavior is by design. The appropriate events are generated if you manually move items into the Sent Items folder.
Please find the following KB article, which provides resolution.