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Disabling New Outlook Access via PowerShell

April 23, 2025 | Operations

Microsoft’s push to transition users from classic Outlook and Windows Mail to the new Outlook app has been met with mixed reactions. For organizations or users preferring to stick with classic Outlook, PowerShell offers a robust way to disable access to the new Outlook app, particularly for work or school accounts managed via Exchange Online. This guide provides step-by-step instructions to restrict new Outlook access using Exchange PowerShell, ensuring your environment remains on the classic version.

Why Disable the New Outlook?

As of 2025, Microsoft has started automatically migrating users to the new Outlook app, with full replacement of Windows Mail and Calendar apps completed by December 2024. While the new Outlook offers a modern interface, it may lack features critical to some workflows or face compatibility issues with non-Microsoft 365 accounts (e.g., Gmail, Yahoo). Disabling access via PowerShell is especially useful for IT admins who want to maintain control over their organization’s email client experience.

Prerequisites

Before proceeding, ensure you have:

  • Admin Access: You need Exchange Online admin privileges to modify mailbox settings.
  • PowerShell Environment: PowerShell 5.1 or later, with the Exchange Online Management module installed.
  • Internet Connection: Required to connect to Exchange Online.

Step-by-Step Guide to Disable New Outlook Access

Follow these steps to disable the new Outlook app for your organization or specific users.

Step 1: Install the Exchange Online Management Module

If not already installed, add the Exchange Online Management module to PowerShell:

Install-Module -Name ExchangeOnlineManagement -Force

Step 2: Connect to Exchange Online

Launch PowerShell as an administrator and connect to Exchange Online:

Connect-ExchangeOnline

You’ll be prompted to sign in with your admin credentials. Follow the authentication steps to proceed.

Step 3: Disable New Outlook for All Users

To prevent all mailboxes from accessing the new Outlook app, run the following command:

Get-CASMailbox | Set-CASMailbox -OneWinNativeOutlookEnabled $false

This command sets the OneWinNativeOutlookEnabled property to false, blocking the new Outlook app from connecting to Exchange Online mailboxes.

Step 4: Disable New Outlook for a Single User

If you only want to restrict specific users, use the user’s email address or identity:

Set-CASMailbox -Identity user@yourdomain.com -OneWinNativeOutlookEnabled $false

Replace user@yourdomain.com with the target user’s email address.

Step 5: Verify the Changes

Confirm that the new Outlook access has been disabled by checking the mailbox settings:

Get-CASMailbox | ForEach-Object { Write-Host "$($_.DisplayName) - OneWinNativeOutlookEnabled: $($_.OneWinNativeOutlookEnabled)" }

This outputs a list of mailboxes and their OneWinNativeOutlookEnabled status. Ensure the value is False for affected users.

Troubleshooting Common Issues

  • “Access Denied” Error: Ensure you have the necessary admin permissions (e.g., Global Admin or Exchange Admin role).
  • Module Not Found: Verify the Exchange Online Management module is installed correctly. Run Get-Module -ListAvailable to check.
  • Changes Not Applying: Microsoft updates may override settings. Re-run the commands after major updates or contact Microsoft support if issues persist.

Additional Considerations

  • Windows Updates: The new Outlook app may still be installed via Windows updates (e.g., KB5051974 in February 2025). To block installation, consider registry tweaks (e.g., setting BlockedOobeUpdaters to ["MS_Outlook"] in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsUpdate\Orchestrator\UScheduler_Oobe).
  • Account Types: This method primarily affects Microsoft 365 work/school accounts. Third-party accounts (e.g., Gmail) may still access the new Outlook unless blocked via other means.
  • User Communication: Inform users about the change to avoid confusion, as they may see prompts to try the new Outlook.

Conclusion

Disabling the new Outlook app via PowerShell is a straightforward way to maintain control over your organization’s email client. By leveraging Exchange Online’s Set-CASMailbox cmdlet, admins can ensure users remain on classic Outlook, avoiding disruptions caused by Microsoft’s migration. Regularly monitor for Microsoft updates that may re-enable the new Outlook, and consider complementary measures like registry edits for a comprehensive solution.

For further assistance or tailored IT solutions, contact the Pacific Bay Tech team at support@pacificbaytech.com.

Tags: Outlook, PowerShell, Exchange Online, IT Administration
Categories: Technical Guides, Microsoft 365