[GH-ISSUE #134] Outlook add-in can no longer authenticate in outdated Outlook versions or in Semi Annual Extended Channel (cloud only) #61

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opened 2026-02-27 20:31:03 +03:00 by kerem · 1 comment

kerem commented

2026-02-27 20:31:03 +03:00

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Originally created by @GruberMarkus on GitHub (Mar 12, 2025).
Original GitHub issue: https://github.com/Set-OutlookSignatures/Set-OutlookSignatures/issues/134

Issue happens in the latest release

I confirm that the issue happens in the latest release of Set-OutlookSignatures

Previously solved issues and documentation

I have searched through issues, discussions and documentation, but have not found an answer to my issue

Code of Conduct

I agree to follow this project's Code of Conduct

What happened?

The Outlook add-in needs to authenticate before accessing mailboxes. In cloud environments only, Microsoft is modernizing add-in authentication from legacy Exchange Online tokens to nested app authentication (NAA).

The Outlook add-in supports both methods, with a fallback mechanism between the two methods.

Microsoft started to slowly disable legacy Exchange Online tokens on a per-user basis, but at the same not all supported Outlook versions meet the requirements for nested app authentication yet. This leads to a situation where the Outlook add-in (and other add-ins) can not authenticate at all.

When one or all of your Exchange Online mailboxes are affected, first make sure that your version of Outlook is still in support and is capable of NAA. See this arcticle for details.

If your Outlook version is not capable of NAA, you should first try to update to a supported version. If this is not possible, you may consider temporarily re-enabling legacy Exchange Online tokens as described here.

In June 2025, Microsoft will disable legacy Exchange Online tokens for good. Make sure to use a supported version of Outlook until this the latest, as nested app authentication will be the only authentication mechanism then.

Originally created by @GruberMarkus on GitHub (Mar 12, 2025). Original GitHub issue: https://github.com/Set-OutlookSignatures/Set-OutlookSignatures/issues/134 ### Issue happens in the latest release - [x] I confirm that the issue happens in the latest release of Set-OutlookSignatures ### Previously solved issues and documentation - [x] I have searched through issues, discussions and documentation, but have not found an answer to my issue ### Code of Conduct - [x] I agree to follow this project's Code of Conduct ### What happened? The Outlook add-in needs to authenticate before accessing mailboxes. In cloud environments only, Microsoft is modernizing add-in authentication from legacy Exchange Online tokens to nested app authentication (NAA). The Outlook add-in supports both methods, with a fallback mechanism between the two methods. Microsoft started to slowly disable legacy Exchange Online tokens on a per-user basis, but at the same not all supported Outlook versions meet the requirements for nested app authentication yet. This leads to a situation where the Outlook add-in (and other add-ins) can not authenticate at all. When one or all of your Exchange Online mailboxes are affected, first make sure that your version of Outlook is still in support and is capable of NAA. See [this arcticle](https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/faq-nested-app-auth-outlook-legacy-tokens#when-is-naa-generally-available-for-my-channel) for details. If your Outlook version is not capable of NAA, you should first try to update to a supported version. If this is not possible, you may consider temporarily re-enabling legacy Exchange Online tokens as described [here](https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/turn-exchange-tokens-on-off). In June 2025, Microsoft will disable legacy Exchange Online tokens for good. Make sure to use a supported version of Outlook until this the latest, as nested app authentication will be the only authentication mechanism then.

kerem

2026-02-27 20:31:03 +03:00

closed this issue
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kerem commented

2026-02-27 20:31:04 +03:00

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@GruberMarkus commented on GitHub (Mar 14, 2025):

The information of this issue has been added to the documentation of release v4.18.1, it is therefore closed.

@GruberMarkus commented on GitHub (Mar 14, 2025): The information of this issue has been added to the documentation of release v4.18.1, it is therefore closed.