Exchange Online token deprecation plan

If you're using Outlook add-ins that rely on legacy Exchange Online tokens, it's time to upgrade to Nested App Authentication (NAA) and Entra ID tokens to avoid breaking when tokens are eventually turned off. Microsoft has deprecated legacy Exchange Online user identity tokens and callback tokens in favor of more secure options as part of the Secure Future Initiative, and a timeline for deactivation is available.

Administrators should identify which add-ins need to be updated and contact the relevant ISVs or developers to obtain updates, while developers must check their add-in code to ensure related API calls are still valid.

It's recommended to implement updates as soon as possible, as add-ins are often essential to mission-critical tasks, and updates may take some time to deploy. By adopting NAA, you'll benefit from simple authentication and top-tier identity protection through APIs bespoke for use in Office hosts.

Note that this change only affects Exchange Online, and add-ins used in on-premises environments will not be impacted.

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