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How to Manage Outlook OST File Size with Group Policy

By: Author Alex Lim

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Learn how to use Group Policy to control the size of Outlook OST files in an Exchange environment and prevent performance issues and corruption.

Outlook OST files are offline copies of your Exchange mailbox data that allow you to access your emails even when you are not connected to the server. However, OST files can grow very large over time and cause problems such as slow Outlook performance, synchronization errors, and file corruption. In this article, we will show you how to use Group Policy to manage the size of Outlook OST files and avoid these issues.

What is the Maximum Size of an Outlook OST File?

The maximum size of an Outlook OST file depends on the version of Outlook you are using. The following table summarizes the default maximum size for different Outlook versions:

Outlook Version Default Maximum Size
Outlook 2002 2 GB
Outlook 2003 20 GB
Outlook 2007 20 GB
Outlook 2010 50 GB
Outlook 2013 50 GB
Outlook 2016 50 GB
Outlook 2019 50 GB
Outlook 365 50 GB

You can also modify the maximum size of an OST file by editing the registry settings, but this is not recommended unless you have a specific reason to do so.

How to Use Group Policy to Manage Outlook OST File Size

One of the best ways to manage the size of Outlook OST files is to use Group Policy. Group Policy allows you to configure various settings for Outlook, such as the cached mode slider, the default location, and the synchronization options. By using Group Policy, you can apply the same settings to multiple users and computers in your domain and ensure consistency and compliance.

To use Group Policy to manage Outlook OST file size, you will need to download and install the Group Policy administrative templates for your version of Office.

After installing the administrative templates, you can follow these steps to configure the Group Policy settings for Outlook OST file size:

  1. Open the Group Policy Management Console (GPMC) on your domain controller or a computer with the Remote Server Administration Tools (RSAT) installed.
  2. Create a new Group Policy Object (GPO) or edit an existing one that applies to the users or computers that you want to manage.
  3. In the Group Policy Management Editor, navigate to User Configuration > Policies > Administrative Templates > Microsoft Outlook 2016 > Miscellaneous > PST Settings.
  4. Double-click the Default location for OST files setting and enable it. Then, specify the path where you want to store the OST files. You can use environment variables, such as %USERPROFILE%, to create a dynamic path for each user. Click OK to save the setting.
  5. Double-click the Force PST path policy setting and enable it. This setting will prevent users from changing the location of their OST files. Click OK to save the setting.
  6. Double-click the Prevent users from adding PSTs to Outlook profiles and/or prevent using Sharing-Exclusive PSTs setting and enable it. This setting will prevent users from creating additional PST files that can consume disk space and cause performance issues. Click OK to save the setting. Double-click the Prevent users from adding PSTs to Outlook profiles and/or prevent using Sharing-Exclusive PSTs setting and enable it. This setting will prevent users from creating additional PST files that can consume disk space and cause performance issues. Click OK to save the setting.
  7. Navigate to User Configuration > Policies > Administrative Templates > Microsoft Outlook 2016 > Account Settings > Exchange > Cached Exchange Mode.
  8. Double-click the Cached Exchange Mode Sync Settings setting and enable it. Then, select the option that suits your needs. You can choose to sync all mail, 12 months, 6 months, 3 months, 1 month, or 2 weeks of mail. The less mail you sync, the smaller the OST file will be. Click OK to save the setting. Double-click the Cached Exchange Mode Sync Settings setting and enable it. Then, select the option that suits your needs. You can choose to sync all mail, 12 months, 6 months, 3 months, 1 month, or 2 weeks of mail. The less mail you sync, the smaller the OST file will be. Click OK to save the setting.
  9. Double-click the Download shared non-mail folders setting and disable it. This setting will prevent Outlook from downloading shared folders, such as calendars and contacts, that are not part of the user’s mailbox. This will reduce the size of the OST file and the network traffic. Click OK to save the setting. Double-click the Download shared non-mail folders setting and disable it. This setting will prevent Outlook from downloading shared folders, such as calendars and contacts, that are not part of the user’s mailbox. This will reduce the size of the OST file and the network traffic. Click OK to save the setting.
  10. Close the Group Policy Management Editor and link the GPO to the appropriate organizational unit (OU) or domain.
  11. Run gpupdate /force on the client computers or wait for the Group Policy to refresh automatically.

Frequently Asked Questions (FAQs)

Question: How to Check the Size of an Outlook OST File?

Answer: To check the size of an Outlook OST file, you can follow these steps:

  1. Open Outlook and click File > Info > Account Settings > Account Settings.
  2. On the Data Files tab, select the OST file and click Settings.
  3. On the General tab, click the Folder Size button.
  4. You will see the total size of the OST file and the size of each folder in the mailbox.

Question: How to Compact an Outlook OST File?

Answer: To compact an Outlook OST file, you can follow these steps:

  1. Open Outlook and click File > Info > Account Settings > Account Settings.
  2. On the Data Files tab, select the OST file and click Settings.
  3. On the Advanced tab, click the Outlook Data File Settings button.
  4. Click the Compact Now button and wait for the process to complete.

Compacting an OST file will remove any unused space and reduce the file size. However, it will not change the amount of mail that is synced to the OST file. To do that, you need to adjust the cached mode slider as explained above.

Question: How to Repair a Corrupt Outlook OST File?

Answer: If your Outlook OST file is corrupt or damaged, you can try to repair it using the ScanPST.exe tool. This tool is located in the Office installation folder, such as C:\Program Files\Microsoft Office\root\Office16. To use the ScanPST.exe tool, you can follow these steps:

  1. Close Outlook and any other applications that use the OST file.
  2. Locate and run the ScanPST.exe tool.
  3. Browse and select the OST file that you want to repair.
  4. Click the Start button and wait for the tool to scan the OST file for errors.
  5. If any errors are found, click the Repair button and wait for the tool to fix them.
  6. When the repair is complete, click OK and close the tool.
  7. Open Outlook and check if the OST file is working properly.

Summary

In this article, we have shown you how to use Group Policy to manage the size of Outlook OST files in an Exchange environment. By using Group Policy, you can control the location, the synchronization, and the prevention of OST files for multiple users and computers. This will help you improve Outlook performance, prevent OST file corruption, and save disk space and network bandwidth.

Disclaimer: This article is for informational purposes only and does not constitute professional advice. You should always consult with your IT administrator before making any changes to your Outlook or Exchange settings. We are not responsible for any damages or losses caused by following the instructions in this article.