I have a number of thin clients at the office. They're on a VM running Windows Server 2008 and Office 2010. The C: drive has 150 GB of space and we use a network storage device for our shared drive where the majority of files are stored.

I ran spacesniffer to see what was taking up the majority of the drive. Spacesniffer identified Outlook as the program that was taking up the majority in the user accounts. I deleted a few users that no longer work for the company or are not using thin clients anymore. It freed up about 20 GB of space. However, I went back to check on the drive, and within 24 hours of freeing up that space, the drive was back to less than 1 GB available.

Any help to clean up some Outlook data would be helpful along with a reason why the drive would fill up so quickly would be greatly appreciated.


It's the OST files... the locally cached copy of the emails and calendar events and such that Outlook downloads from the Exchange server.

You want to disable cached mode and prevent Outlook from creating an OST file, though why you'd do this instead of just using OWA (Outlook Web App/"Exchange Webmail") is beyond me.

Both settings are controllable by GPO or registry key, so pick your preferred method.

These policies will set the following registry values

HKEY_CURRENT_USER\Software\Policies\Microsoft\office\15.0\outlook\cached mode
DWORD: enable
Value: 0

Value: 2

NoOst value specifies whether or not an OST is created at startup. Setting the NoOst value to 2 will prevent the use of OST files. A value of 3 will allow OST files for cached mode but won't create one when online mode is used.

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