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We had a user today ask us why emails in their deleted folder were mysteriously being deleted. While investigating we learned that we've got 5-day auto-clean enabled for the Junk and Deleted folders (which is probably the default and a good one to have), however, neither the domain administrator nor the user have the ability to see what rules are in place when they are using the "default". When somebody then chooses to override in order to take a look at the existing rules, it clears the list of rules so you can't figure out what they were either.
So my suggestion on the Settings -> Filtering -> Folder Auto-Clean settings page, that if the current setting is to use the "default settings" (wherever they're coming from) that those default settings are listed somewhere so people can make an informed decision about whether or not they'd want to override those rules.