Microsoft Notifies of Major Domain Change With Teams is Coming

In April 2023, Microsoft announced that it would be undertaking a multi-year effort to reduce domain fragmentation among authenticated, user-facing Microsoft 365 apps and services by bringing them onto a single, consistent and cohesive domain:

This consolidation will help improve security, administration, and user experience across the board, and will ultimately lay a foundation for better and tighter integration across the Microsoft 365 ecosystem.

As we prepare to migrate the Teams, Outlook, and Microsoft 365 web apps to the domain, developers of Teams apps – including those that run on Outlook and Microsoft 365 – need to take the actions described below to ensure that those apps continue to function on the new domain.

If no action is taken, your app may not render in the new domain ( when it goes live in June 2024.

If you are unable to update your app before that time, any tenant running your app will remain on while we work with you to make the necessary changes.

This change impacts embedded applications where an external web app is rendered inside Teams, Outlook, or Microsoft 365. If your app falls into this category, it will be affected.

How To Prepare Your App For cloud.Microsoft

Today, apps that embed their web content in a Microsoft 365 host application such as Teams, Outlook, or run on a set of inherently trusted domains that are hardcoded in the TeamsJS client library.

To support the rollout of applications under domain and make future cross domain app integration more seamless, Microsoft will migrate this list of trusted domains to a new CDN endpoint to be called on app initialization.

This change was released in early January 2024 as part of Teams JS version 2.19 release. This new list will be dynamic, which will limit the impact of any future domain changes on your app.

To avoid any breaking changes to your app in the new domain, you will need to perform the following actions:

  1. Upgrade Teams JS library to version 2.19 or higher.
  2. Update your x-frame-options/CSP headers to allow for the new domains. To ensure the app keeps working across existing and future Microsoft 365 hosts, please ensure to allow “*”.

Timeline And Impact:

To prepare your app for the transition to, please complete the changes above as soon as you are able.

The domain is now available for testing, with full operation alongside expected in June. At that time, the expected user experience will be as follows:

App opened in

  • Everything will work as expected.

App opened in

  • CTAs complete: Everything will work as expected.
  • CTAs not complete: Error message given with guidance for the user to navigate to to use the app.

The transition to will benefit users and developers across the Microsoft 365 ecosystem.

We are excited to take the next steps toward bringing Teams, Outlook, and Microsoft 365 onto the unified domain, and extending those benefits to app developers as well.

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