The HTTP request was forbidden with client authentication scheme
As of March 24th, 2026, new occurrences of this issue have been reported. Veeam and Microsoft are working together to isolate and resolve the issue. Further updates will be provided as more information becomes available.
- Update 2026-03-26
It appears some cases may be related to preemptive disablement of EWS access. Please review "Control access to EWS in Exchange" and manually configure EWS access using PowerShell.
Note: The default value forGet-OrganizationConfig -EwsEnabledis$null. We recommend you set this toSet-OrganizationConfig -EwsEnabled $trueuntil the phase-out period to avoid possible service interruptions.
Microsoft has announced that, as of the end of June 2026, EWS access will be deprecated for the following licenses:
- Exchange Online Kiosk
- Microsoft 365 and Office 365 F1
- Microsoft 365 and Office 365 F3
For more information, see: Update to EWS Access for Kiosk/Frontline Worker Licensed Users.
Challenge
Microsoft 365 backups display the following error:
The HTTP request was forbidden with client authentication scheme 'Anonymous'.
This error typically occurs when specific mailboxes are accessed during backup jobs.
Cause
Following a coordinated investigation with Microsoft, we have confirmed that certain subscription plans, such as Exchange Online Kiosk and similar limited-service SKUs, may not support the API required by Veeam Backup for Microsoft 365.
As a result, calls to the API return an HTTP 403 Forbidden error, causing backup jobs to fail.
Solution
Status: This issue is resolved as of December 2025.
Issue Root Cause: Mailboxes licensed with Exchange Online Kiosk, Microsoft 365, and Office 365 F1, and Microsoft 365 and Office 365 F3, were temporarily blocked from accessing the API used by Veeam for backup operations. The access has been restored, and the issue has been resolved.
For more information, please refer to the following Microsoft article: Update to EWS Access for Kiosk / Frontline Worker Licensed Users.
Veeam R&D continues to work closely with Microsoft on the upcoming deprecation of the EWS API. A future update will address these changes. A Veeam Support Statement regarding EWS deprecation is available on KB4820.
If this KB article did not resolve your issue or you need further assistance with Veeam software, please create a Veeam Support Case.
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