Summary
Details
Updated July 28, 2025: We have updated the content, timeline, and additional resources.
We are changing the recommended method for disabling Outlook for the web so that users can continue to access the new Outlook for Windows.
[When this will happen:]
There is no change that is rolling out. We have published a new support article with instructions on how to use our existing infrastructure to block users from access Outlook for the web without impacting Outlook for Windows.
[How this will affect your organization:]
Admins can follow the instructions in this support article to block access to Outlook for the web using Conditional Access. Blocking Outlook for the web using this policy has no impact on Outlook for Windows.
Once Outlook for the web is blocked, admins can set the CASMailbox policy -OWAEnabled to $true. This will have no impact on users' ability to access outlook for the web since the work was already done to block Outlook for the web with another policy.
[What you need to do to prepare:]
There are no changes to existing polices, so there is nothing you need to do to prepare.
Learn more
- Enable or disable Outlook on the web access to mailboxes in Exchange Server | Microsoft Learn (will be updated before rollout)
- Enable or disable access to the new Outlook for Windows | Microsoft Learn (will be updated before rollout)
#newoutlookforwindows
Change History
Updated May 8, 2025: We have updated the timeline below. Thank you for your patience.
We are changing how you enable or disable the new Microsoft Outlook for Windows and Microsoft Outlook for the web.
[When this will happen:]
General Availability (Worldwide, GCC): We will begin rolling out late June 2025 (previously late April) and expect to complete by mid-July 2025 (previously mid-May).
[How this will affect your organization:]
We're changing the CASMailbox -OWAEnabled parameter that enables or disables access to user mailboxes using Outlook for the web (formerly known as Outlook Web App or OWA) to block only Outlook for the web and to not affect the behavior of new Outlook for Windows.
You can manage new Outlook for Windows with the CASMailbox-OneWinNativeOutlookEnabled policy.
You are receiving this message because our reporting indicates one or more users in your organization may be using the New Outlook for Windows.
Note: We will not change any existing value for the settings, but we will change which setting controls if the new Outlook for Windows is allowed for the user. Before this rollout, both CASMailbox-OWAEnabled and CASMailboxOneWinNativeOutlookEnabled policies are checked. After this rollout, we will remove the check for CASMailbox-OWAEnabled so you can have the chance to enable new Outlook and still disable Outlook for the web if desired.
[What you need to do to prepare:]
This rollout will happen automatically by the specified date with no admin action required before the rollout. Review your current configuration to determine the impact for your organization. You may want to notify your admins about this change and update any relevant documentation.
After this change takes effect, please confirm the CASMailbox OneWinNativeOutlookEnabled policy state for each mailbox. The default value is Enabled.
Learn more
- Enable or disable Outlook on the web access to mailboxes in Exchange Server | Microsoft Learn (will be updated before rollout)
- Enable or disable access to the new Outlook for Windows | Microsoft Learn (will be updated before rollout)
#newoutlookforwindows
Updated July 28, 2025: We have updated the content, timeline, and additional resources.
We are changing the recommended method for disabling Outlook for the web so that users can continue to access the new Outlook for Windows.
[When this will happen:]
There is no change that is rolling out. We have published a new support article with instructions on how to use our existing infrastructure to block users from access Outlook for the web without impacting Outlook for Windows.
[How this will affect your organization:]
Admins can follow the instructions in this support article to block access to Outlook for the web using Conditional Access. Blocking Outlook for the web using this policy has no impact on Outlook for Windows.
Once Outlook for the web is blocked, admins can set the CASMailbox policy -OWAEnabled to $true. This will have no impact on users' ability to access outlook for the web since the work was already done to block Outlook for the web with another policy.
[What you need to do to prepare:]
There are no changes to existing polices, so there is nothing you need to do to prepare.
Learn more
- Enable or disable Outlook on the web access to mailboxes in Exchange Server | Microsoft Learn (will be updated before rollout)
- Enable or disable access to the new Outlook for Windows | Microsoft Learn (will be updated before rollout)
#newoutlookforwindows
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