What does the AutoArchive setting's Delete expired items when AutoArchiving option on email folders do?
To configure an expiration date for the message, click Options to open the Message Options dialog box, which Figure 3 shows, then use the Expires after check box (under Delivery options). By default, Outlook shows an expired message in gray strikethrough text in the recipient's Inbox. That folder's AutoArchive settings determine what happens to expired items when Outlook archives messages. If the recipient has selected the Delete expired items when AutoArchiving check box, Outlook will delete expired items. If the recipient has cleared the check box, Outlook will save the expired items to the target archive folder.