How to Fix Cached Exchange Mode is Greyed Out in Outlook?

CEM – Cached Exchange Mode – is a feature in MS Outlook that downloads and stores all your mailbox locally on your device in an OST file, and allows you to search, draft, or read your emails even without the internet connection. This mode is available only when you configure Outlook with Exchange Server, Outlook.com, and Microsoft 365 accounts.  

(See: What is Cached Exchange Mode)

However, At times, you find that the Cached Exchange Mode option is greyed out in Outlook, meaning the checkbox is disabled. This usually happens when your email client cannot verify that the account supports Cached Exchange Mode or when feature has been turned off by an administrator through Group Policy or registry settings. In this post, we will explain the ways to fix Cached Exchange Mode – CEM – is greyed out issue.

Root Causes: Why is Cached Exchange Mode Greyed Out?

The table below covers the root causes of CEM option being greyed out issue.

Note: Terminal Services / Remote Desktop is a permanent limitation — Microsoft deliberately disables CEM in RDS environments. No registry edit or GPO change can enable CEM on Terminal Services.

Which Fix should you Use? 

Refer to the table below and choose the right fix based on your situation:

Solutions to Fix the Cached Exchange Mode is Greyed Out Issue in Outlook

Follow the solutions mentioned below to fix the issues and enable Cached Exchange Mode in Outlook.

Fix 1: Check Account Type

Cached Exchange Mode is a feature in Outlook which works only with Exchange and Microsoft 365 accounts. You will find this option greyed out, if you’ve configured your Outlook with IMAP or POP3 mail account as these do not support this feature. Follow the steps mentioned below to confirm this:

• Open Outlook.
• Go to File.
• Click Account Settings > Account Settings.

• Click on the Email tab.
• Read the Type column for your email account.

• If the account type displays ‘IMAP’ or ‘POP/SMTP’, CEM is unavailable. If it shows ‘Microsoft Exchange’, proceed to other fixes.

Fix 2: Check and Modify Group Policy (IT Admins)

Several organizations manage the Outlook settings through Group Policy. If a GPO – Group Policy Object – is configured to disable Cached Exchange Mode, the option will appear greyed out in Outlook. You cannot change these settings — only IT admins can modify them.

You can follow the below steps to check if Group Policy is causing the issue:

• Open Command Prompt as an administrator.
• Run this command:
• gpresult /h C:\GPReport.html 

• Once the report is generated, open C:\GPReport.html in a web browser.
• Search for terms such as:
• Cached Exchange Mode
• Microsoft Outlook, or
• Exchange.
• If you find a policy that disables CEM, contact your IT administrator and request a policy review.

How IT admins can enable CEM via GPO?

An administrator can update the policy settings by following these steps:

• On the domain controller or a machine with Group Policy Management Console – GPMC, open GPMC.
• Go to the GPO applied to the affected users:
• User Configuration > Policies
• Select Administrative Templates > Microsoft Outlook
• Click Account Settings > Exchange
• Select Cached Exchange Mode.
• Look for policies such as:
• Use CEM for new and existing Outlook profiles.
• Disable “Cached Exchange Mode” for new and existing Outlook profiles.
• Set the policy to Not Configured or Enabled.
• Run gpupdate /force on the user’s machine, or wait for the next GPO refresh cycle (90 minutes by default).
• Verify that the CEM checkbox is now available in your Outlook Account Settings.

Source: Group Policy template for Outlook. Visit –  Microsoft Learn: Configure Cached Exchange Mode

Fix 3: Edit the Registry Key to Enable Cached Exchange Mode

At times, this Outlook feature gets disabled due to altered registry keys. By editing the registry keys, you can turn on or off the CEM option. Here’s how: 

See the complete backup process here.

Note: Registry editing can cause system issues if done incorrectly. Back up the registry before making changes: File > Export in Registry Editor.

• Press Windows + R.
• Type regedit, and press Enter.
• Navigate to:
• HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\x.0\Outlook\Cached Mode (replace x.0 with your Outlook version: 15.0 = 2013, 16.0 = 2016/2019/365).
• Look for a DWORD value named Enable or Disable.
• If you see a ‘Disable’ key with value 1, double-click it and change the value to 0.
• If you see an ‘Enable’ key with a value of 0, double-click it and change it to 1.
• If the ‘Cached Mode’ key does not exist under Outlook, navigate to: 
• HKCU\Software\Microsoft\Office\x.0\Outlook\Cached Mode and create a new DWORD named Enable with value 1.
• Close Registry Editor.
• Restart Outlook.
• Go to File.
• Click Account Settings > Account Settings.
• Select your Exchange account.
• Click Change.

The ‘Use Cached Exchange Mode’ checkbox should now be available.

Outlook version registry path reference:

Note: If the CEM setting is managed by GPO, then it may revert to its policy value at the next GPO refresh cycle. In such a case, Fix 2 – changing the GPO – is the only permanent solution.

Fix 4: Create a New Outlook Profile

Corruption in Outlook profile can also cause the cached mode greyed out issue. So, recreate your profile to fix this problem. The steps are as follows:  

• Go to Control Panel.

• Click User Accounts > Mail.
• Tap on Show Profiles. 
• Select Add.

• Enter or type the Profile Name.
• Click OK.
• Complete the account sign-in process by entering your email credentials.
• After signing in, open Outlook.
• You will see a dropdown. Choose your new profile from the dropdown.
• Click OK.

Now, check and enable the Cached Exchange Mode. For this,

• Go to File > Info.
• Click on Account Settings > Account Settings.
• Select your email account.
• Click Change.
• Check or tick the Use Cached Exchange Mode option.
• Click Next > Finish.
• Restart Outlook.

Fix 5: Switch from New Outlook to Classic Outlook

New Outlook uses a cloud-based synchronization model and does not support Cached Exchange Mode option. If you are using New Outlook, you need to switch to Classic version to modify the CEM setting. Here’s how:

• Open New Outlook.
• In the upper-right corner of the Outlook window, locate the New Outlook toggle.
• Turn the toggle Off.
• Outlook will close and reopen in Classic Outlook.
• Now go to File.
• Click Account Settings > Account Settings.
• Select your Exchange/Microsoft 365 account.
• Click Change.
• Now you can see the Cached Exchange Mode option.
• Click the checkbox to enable or disable it.

Note: Switching from New Outlook to Classic version does not remove any mailbox data. Only the interface and feature set are changed. Also, you can switch back to the New Outlook anytime.

Fix 6: Resolve Microsoft 365 Account — Modern Authentication Issue

Outlook – in some Microsoft 365 setups – may not identify the account correctly. This usually happens if you’ve done changes to Microsoft 365 settings, authentication methods, or account configuration. It can cause Cached Exchange Mode – CEM – to be unavailable because Outlook does not recognize the account as Exchange-compatible. You can fix this issue by re-adding your account. Here’s how:

1: Sign Out of Outlook

• Open Outlook.

• Go to File > Office Account.

• Click Sign Out.

2: Remove the Existing Account

• Go to File > Account Settings > Account Settings.

• Select the affected account.

• Click Remove.

3: Add the Account Again

• Restart Outlook.

• Add the account using your Microsoft 365 email address.

• Allow Outlook to automatically configure the account through Autodiscover.

 4: Verify the Account Type

After the setup is complete, confirm that Outlook recognizes the account as a Microsoft Exchange account and not IMAP.

• Go to File > Account Settings > Account Settings.

• Select the account and click Change.

• Verify that the account type is displayed as Microsoft Exchange.

Now, check whether the Use Cached Exchange Mode option is now available.

What if some Outlook Data is Missing after Re-enabling Cached Exchange Mode?

You may experience missing mailbox items after re-enabling CEM – Cached Exchange Mode – or creating a new Outlook profile. This might happen because the email client creates new OST file for the new profile. This file starts as a fresh local cache and synchronize data from the server. It does not transfer items from the older OST file.  

(See: How to Reset Local Cache in Outlook)

So, for recovering the missing items, you have to convert your old OST file into PST format. As this OST is not accessible via Outlook, you have to use Stellar Converter for OST – an advanced OST to PST converter tool. It can help you to selectively extract mail items – emails, contacts, calendars, etc. – from the OST and save them to PST format. You can then open/import the converted file into your Outlook account. This tool can also save the OST file items in formats like HTML, PDF, etc.

Conclusion

You may encounter “Cached Exchange Mode appearing greyed out” issue in Outlook due to unsupported account type, Group Policy restrictions, registry settings, profile corruption, or limitations associated with New Outlook. Based on the cause, you can apply the solution – mentioned in this guide – to resolve the problem.