How to Turn Off Cached Exchange Mode for Microsoft 365 Shared Mailboxes?

Cached Exchange Mode is the default mode in Microsoft 365, Outlook.com, Microsoft Exchange, and IMAP Server accounts. This mode enables the users to access their mailbox data, such as emails, contacts, calendars etc., when they are not connected to the Internet. This mode particularly helps when you’re in a place with a patchy Internet connection or facing other connectivity issues.

While this is convenient, this also has some disadvantages. In particular, if you use one or more shared mailboxes and access them with the same Outlook profile, it increases the size of the locally saved OST file. Quickly, the OST file can exceed the recommended size limit of 50 GB. When this happens, you start experiencing issues, like slow Outlook performance issues, delays in sending and receiving emails, Outlook freezing or not responding, new emails not showing, and more. Sometimes, The attempt to log on to Microsoft Exchange has failed, and the OST can also become inconsistent or corrupted.

To avoid these issues, you can turn off the Cached Exchange Mode for the shared mailbox. It helps prevent the OST file from growing beyond the recommended limit. Turning off cached mode can also remove potential sync issues and other Outlook performance-related issues.

However, there is no need to turn off the Cached Exchange Mode for the entire account. Microsoft offers the option to turn off the cached mode for shared mailboxes only.

Ways to Turn Off Cached Exchange Mode for Shared Mailboxes

Here are some ways that you can use to turn off Cached Exchange Mode for shared mailboxes.

1. Turn off Cached Exchange Mode using Outlook

To turn off the Cached Exchange Mode for shared mailboxes in different Outlook versions, follow these steps.

For Outlook 2013, 2016, 2019, and 2021

• Go to File > Account Settings > Account Settings.

• Select your Exchange or Microsoft 365 account from the list under the Email tab and click Change.
• On the Change Account screen, go to More Settings.
• Under the Advance tab in the Microsoft Exchange window, uncheck the “Download Shared folders or Download Public Folder Favorites” checkbox.

• Click OK and restart Outlook.

Note: If you like to make some parts of the emails available offline, click the “More Settings” option and specify the period for which data will be saved in the OST file.

For Outlook 2010

• Go to File > Account Settings > Account Settings.
• Select your Exchange or Microsoft 365 account from the list under the Email tab and click Change.
• Uncheck the “Download Shared Folders” checkbox.
• Restart Outlook.

2. Turn off Cached Exchange Mode through Registry Editor

You can also turn off the Cached Exchange Mode through the Registry Editor. Here are the steps:

• Press Windows + R keys. In the Run dialog box, type regedit. This opens the Windows Registry.
• Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\VERSION\Outlook\Cached Mode.
• Create a new DWORD registry CacheOthersMail and enter the value 00000000.
• Close the Registry Editor window and restart Outlook.

Note: If the Cached Mode key is not available, right-click on Outlook and choose New to create the key.

3. Turn off Cached Exchange Mode using Group Policy

If you’re an administrator, you can disable the Cached Exchange Mode through the Group Policy. However, to use this, you must install the Administrative Template Files (ADMX/ADML) on the Exchange Server. Once you have downloaded the template, follow the below steps to turn off the Cached Exchange Mode:

• Copy the ADMX file to C:\Windows\PolicyDefinitions and the ADML file to C:\Windows\PolicyDefinitions\en-US.

• Open the Group Policy Management. To do this, open the Run dialog box (press Windows + R) and type gpmc.msc.
• In the Group Policy console, right-click on the Organizational Unit (OU) to which you want to apply this policy. Select the “Create a GPO in this domain and link it here” option.
• Enter the name of the policy and click OK.
• Next, right-click on the GPO you just created and select Edit.
• Now, create a new GPO. To do this, head to User Configuration > Policies > Administrative Templates > Microsoft Outlook 201x > Outlook Options > Delegates.
• Double-click the Disable shared mail folder caching policy.
• In the left-hand pane, select the “Enabled” radio button.
• Click Apply > OK.

Now, ask the users to restart Outlook.

This option is highly effective for disabling the caching of shared mailboxes in the most recent Outlook versions, including Outlook 2021.

Conclusion

Turning off the Cached Exchange Mode for shared mailboxes in Microsoft 365 helps prevent OST files from growing large and improves user productivity. In case, your OST file is inaccessible due to its large size, the easiest option is to use a third-party OST to PST converter software like Stellar Converter for OST. This tool can recover data from an inaccessible or orphaned OST file, and save it in PST and other readable file formats, like PST, EML, RTF, MSG, PDF, and HTML. You can even export the data from the OST file directly to Microsoft 365. This way, you will not lose any data due to an oversized OST file.