Google Apps Admin Access User Drive. Admin should enable in domain wide settings for gmail. Whether the app is authorized to access data on the user's drive.
This feature will be available by default. Hover over a shared drive and click manage members. (optional) to change the access level of a user or remove them from the shared drive, next to the user, click the down arrow and choose an option.
Google apps for work accounts give each user 30gb of space, while google apps unlimited does not put any restriction on the space available to your users.
You could also try vembu saasbackup solution for gsuite, where in you can backup and restore other user's email available in any folder to another user or your user's inbox. Make sure that drive is turned on for your organization.; Protect your organization with security analytics and best practice recommendations within the security center. You get to know about the file's mime type, the size of the file (handy if you are running out of storage space in drive), the kind of access other users have on your files, the full path of the file in your google drive and the list of google accounts that have access to your files.
