When an end user deletes messages from backup storage, by default, those deleted messages are still on the production Exchange server. Commvault software can remove deleted messages from the production Exchange server during the next backup after the messages are deleted from the secondary storage using End-User Delete. This is called source pruning.
When source pruning is configured, the deleted messages appear in Microsoft Outlook until the next incremental backup job deletes them from the Exchange server.
To prevent stubs from becoming orphaned (that is, a stub with no corresponding backed up message) in production Exchange mailboxes, you should enable source pruning when End-User Delete is enabled.
You can configure source pruning for all subclients on a client computer, or for individual subclients.