VMware Horizon: manage Outlook OST files


In a typical non-persistent Horizon environment, to manage the Microsoft Outlook OST files can be challenging if you don't use a correct configuration for your VDI.

Office 365 users have the issue of losing the Outlook OST files each time they log off because the VD is destroyed and the virtual desktop reset to default.

To manage OST files, two additional components must be installed in your Horizon infrastructure:

  • VMware App Volumes
  • VMware DEM


Outlook OST files

Generally, the Microsoft Outlook OST file is stored on the local drive C: of the computer.

In a non-persistent VDI environment, at each logoff the VD is reset to the default settings deleting the OST file. To retain the Outlook cache, a specific configuration is required in your VDI environment.


Install VMware App Volumes

If the Outlook cache file is missing, it will be created each time the user opens the application making the logon process time consuming. To avoid that OST file is recreated each time, the system needs a persistent disk associated with the users where to store the OST file. This is where App Volumes come into play.

To properly deploy App Volumes in your Horizon infrastructure, you can follow this guide.


When Writable Volumes have been configured and assigned to users, after logging in to the virtual desktop the C:\SnapVolumesTemp\writable folder will be "attached" to the VM. To specify where the OST file should be stored you need to configure the system accordingly.


Install VMware DEM

To manage the OST location, VMware DEM is the tool to use. Check out this guide to install and configure DEM.


When the VMware DEM tool has been installed, it must be configured to properly manage Outlook OST files.


Configure DEM to manage OST files

The OST file location can be configured in DEM in two ways:

  • ADMX-based Settings
  • App Volumes


ADMX Templates

To manage the OST location in Outlook, you need to first download the appropriate Office ADMX templates from Microsoft website.


Open the VMware DEM console, go to User Environment tab and select ADMX-based Settings. Click Manage Templates ADMX.


Click Add Folder.


Click Browse and select the folder with the ADMX templates previously downloaded. Click OK.


The ADMX templates have been imported successfully. Click OK.


Click Validate to check if everything is fine with the imported templates.


Click OK.


Click Close.


Make sure ADMX-based Settings is still selected and click Create.


Enter a Name and optionally a Label then click Select Categories.


Expand Microsoft Outlook 2016 and select PST Settings under Miscellaneous. Click OK.


Click Edit Policies.


Select PST Settings and double click in the right side the Default location for OST files item to edit.


Check Enable to enable the policy and enter C:\SnapVolumesTemp\writable in the Default location for OST files field. Click OK.


The Default location for OST files policy is now enabled. Click the X in the upper right corner to close the window.


Click Save to save the configuration.


VMware DEM is now configured to manage Outlook OST files.



App Volumes

Open the VMware DEM console, go to User Environment tab and select App Volumes. Click Create.


Enter a Name for the policy. Check the Store Offline Outlook Data File (.ost) on writable volume option and click Advanced. By default the Root folder points to the standard Writable Volume path. Leave default Sub folder path and click OK then Save.


La policy has been created.



Test the configuration

Login to a Horizon virtual desktop and open Microsoft Outlook. The OST cache file is created by the application.


Checking the Outlook configuration, the OST data location is stored in the configured Writable Volume.


Using the Windows Explorer check the C:\SnapVolumesTemp\writable folder content. You should now find the OST file.


This configuration allows to retain the OST files in a non-persistent VDI environment speeding up the login process.



  1. Praveen 23/09/2022
  2. Mark L 04/10/2023
  3. Kervin 06/03/2024