Controlling PSTs through Regedit

All credit goes to the Microsoft article. Just posting here in case the post disappears.
https://support.microsoft.com/en-us/help/3058474/how-to-use-outlook-policy-to-control-pst-use-and-creation-in-the-offic

Prevent users from adding new data or content 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. To do this, follow these steps:

1. Open Registry Editor.
2. Locate, and then click the following registry subkey:
   HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\<x>.0\Outlook\PST
   Note The <x>.0 placeholder represents the version of Outlook: for example, 15.0 is Outlook 2013, 14.0 is Outlook 2010, and 12.0 is Outlook 2007.
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type PSTDisableGrow, and then press Enter.
5. Right-click the PSTDisableGrow registry entry that you created, and then click Modify.
6. In the Value data box, type 1, and then click OK.

Note The PSTDisableGrow registry entry can be set to the following values:

Value	Description
0	User can add new items to an existing .pst file. This is the default value.
1	Use cannot add new content or data to an existing .pst file

Prevent users from adding 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. To do this, follow these steps:

1. Open Registry Editor.
2. Locate, and then click the following registry subkey:
   HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\<x>.0\Outlook
   Note The <x>.0 placeholder represents the version of Outlook: for example, 15.0 is Outlook 2013, 14.0 is Outlook 2010, and 12.0 is Outlook 2007.
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type DisablePST, and then press Enter.
5. Right-click the DisablePST registry entry that you created, and then click Modify.
6. In the Value data box, type 1, and then click OK.

Note The DisablePST registry entry can be set to the following values:

Value	Description
0	Users can add .pst files. This is the default value.
1	Users cannot add .pst files. However, in scenarios where a .pst file was connected to Outlook before this registry value was added, the existing .pst file will still be connected. No new.pst files can be added.
2	Users can only add exclusive sharing .pst files, such as SharePoint .pst files.