When transitioning to the newer version of Exchange and implementing retention policies, sub-folders will still be available for users. However, it's important to note that managed folders, which were part of the older Messaging Records Management (MRM) system, are deprecated in Exchange Server 2013 and are not supported in newer versions. Instead, retention policies and retention tags will be used to manage email lifecycle, and these can still accommodate sub-folders within user mailboxes.
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