How To Prevent Outlook from Creating Offline OST Cache

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Creating this registry value on the computer will stop Outlook from enabling offline cache (OST). This will apply to all users on the computer since the registry key is in Local Machine. This is helpful especially on terminal servers (Remote Desktop Services – RDS) so that OST files from multiple users don’t eat up disk space. Does not require a reboot to take affect.

Create this key: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\OST

Create a value in that key called NoOST of type REG_DWORD and set the value to 2.

Create any of the keys that don’t exist.

Change the version above to the version of Outlook you’re using (14.0 for Outlook 2010, 15.0 for Outlook 2013, or 16.0 for Outlook 2016 and Outlook 365 App).

See here for more detail: including other value possibilities for NoOST.


Jason works as a project specialist at an IT MSP in Pennsylvania, USA. He's an IT/security professional with 20 years experience.