Use a policy to control PST files in Outlook

In Microsoft Outlook, users can create PST files or add new items to existing PST files. This article describes how to control these behaviors.

Important

This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For protection, back up the registry before you modify it so that you can restore it if a problem occurs. For more information about how to back up and restore the registry, see How to back up and restore the registry in Windows.

Prevent additions to an existing PST file

To prevent users from adding new data or content to an existing PST file, add the PSTDisableGrow registry entry, and then set the value to 1. Use the following steps:

1. Open Registry Editor.

2. Select either of the following registry subkeys depending on whether you want to deploy the setting through Group Policy (GPO) or the Office Customization Tool (OCT). Create the subkey if it doesn't exist.

   Type	Registry path
   GPO	HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook\PST
   OCT	HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\PST

3. On the Edit menu, select New > DWORD Value.

4. Enter PSTDisableGrow, and then press Enter.

5. Right-click the PSTDisableGrow registry entry that you created, and then select Modify.

6. In the Value data box, enter 1, and then select OK.

Note

You can set the PSTDisableGrow registry entry to either of the following values:

• 0: Users can add new items to an existing PST file (default value).
• 1: Users can't add new content or data to an existing PST file.

Prevent the addition of new PST files

To prevent users from connecting a PST file to Outlook, add the DisablePST registry entry, and then set the value to 1. Use the following steps:

1. Open Registry Editor.

2. Select either of the following registry subkeys depending on whether you want to deploy the setting through Group Policy (GPO) or the Office Customization Tool (OCT). Create the subkey if it doesn't exist.

   Type	Registry path
   GPO	HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\16.0\Outlook
   OCT	HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook

3. On the Edit menu, select New > DWORD Value.

4. Enter DisablePST, and then press Enter.

5. Right-click the DisablePST registry entry that you created, and then select Modify.

6. In the Value data box, enter 1, and then select OK.

Note

You can set the DisablePST registry entry to any of the following values:

• 0: Users can add PST files (default value).
• 1: Users can't add PST files. However, in scenarios in which a PST file was connected to Outlook before this registry value was added, the existing PST file will remain connected. No new PST files can be added.
• 2: Users can only add PST files that are exclusively for sharing, such as SharePoint PST files.

Considerations for new Outlook

The Group Policy (GPO) and the Office Customization Tool (OCT) registry keys that are described in this article are intended to control PST behavior in classic Outlook for Windows only. However, if organizations want to enable PST functionality for users in new Outlook, they might experience more restrictive behavior due to the presence of these registry keys for classic Outlook. This is because new Outlook for Windows currently relies on classic Outlook's MAPI components to interact with PST files.

Note

The only supported way to control or restrict access to PST files in new Outlook is to set the OwaMailboxPolicy OutlookDataFile parameter. We strongly recommend that administrators explicitly review and set this policy, rather than attempting to rely on classic Outlook registry keys to manage PST files in new Outlook.
To ensure that your organization’s OwaMailboxPolicy is being respected in new Outlook on managed devices, administrators must set the policy to require that new Outlook’s primary account matches the account used to sign in to Windows.

Interaction with Exchange Online policies

If you run the Set-OwaMailboxPolicy cmdlet to set the OutlookDataFile parameter to Allow, which is the default value, Exchange Online policy normally allows users to open, import, export, and copy items to and from PST files. However, if the PSTDisableGrow registry entry is set to 1, it might override the Exchange Online policy for PST file actions in new Outlook clients, in some situations. You'll see the following issues in new Outlook:

• Users can't move mailbox items to a PST.
• Users can't remove PSTs from the mailbox.
• Users can't check PST content.

Tip

If you intend to allow users to fully manage PST files in new Outlook, set the OutlookDataFile parameter to Allow, and ensure that the legacy registry keys, PSTDisableGrow and PSTDisableGrowAllowAuthenticodeOverrides, are either not configured, or are set to their default value (0). This will prevent unintended conflicts and ensure the desired PST file behavior.