Mailbox errors: The HTTP request was forbidden with client authentication scheme 'Anonymous'.

[aeph]

Hi all,

since today we are getting strange error messages on Mailbox-objects: "The HTTP request was forbidden with client authentication scheme 'Anonymous'.".

We haven't changed anything - not all Mailbox objects are affected.

We are running on 8.1.2.3301 - modern application setup is used.

Does anyone else have this problem?

CaseID: #07892767

[megawatt_ak]

same problem arose yesterday 11/18/25 ... 1 user ...

ver 8.1.2.180

Following for the fix

[ReKe]

We are on 8.2.0.2202 and see it also with Veeam Data Cloud.

Case # 07892442

[DaStivi]

I’ve also noticed a few jobs/customers starting to fail with this new error — only a handful so far, but it’s concerning.

[rsk@mb-solutions.dk]

Also seeing this error on 1 of our many customers.

[aeph]

Has anyone been able to find a solution or fix the error? Veeam suggests reauthenticating the organization, but this would require the customer's assistance (global admin).

[MSavp]

We see the same problem with some of our M365 items. Some do seem to be working though. We have v8.1.2.180 installed.

[cfrank@ipn-wi.com]

we are also experiencing this issue on two random utility mailboxes. They do have full user licenses, but users do not use them.

we are on veeam for 365 version 8.2.0.2008

[kshelton]

Following - I have re-authenticated via the app certificate and received the same error. Version 8.2.0.2202

[Dynamic]

Has anyone been able to find a solution or fix the error? Veeam suggests reauthenticating the organization, but this would require the customer's assistance (global admin).

I ran into the same problem today at a customer. Did a re-auth... Didn't fix the problem.
Installing now the update to v8.2.0.2202

[DaStivi]

issue definitely occur on 8.2.0.2202 too..
hadn't had the change on a affected customer to re-auth.

more likely Microsoft just changed something again, as of a couple of weeks ago, just after 8.2 release...

[Mildur]

Hi,

Can you please provide us with your case number (as requested by our forum policy)?

Unfortunately, a simple “+1” does not help us resolve potential issues. Please do not ignore our forum policies. :-)

Thank you,
Fabian

[Polina]

Hi All,

Thanks for the heads-up. The issue is now escalated to RND for investigation. Together with Fabian we'll keep you posted on the updates.

[ReKe]

Maybe it has something to do with issue or not.

The mailboxes we see failling (Onprem and VDC) has all "Online-Kiosk" - Licesnes.

What licsenses do you see failling with this error?

[MSavp]

Maybe it has something to do with issue or not.

The mailboxes we see failling (Onprem and VDC) has all "Online-Kiosk" - Licesnes.

What licsenses do you see failling with this error?

Nice catch!
For us only mailboxes with "Exchange Online Kiosk" licenses failed as well.

[FSOC]

We are also experiencing problems with mailboxes using "Exchange Online Kiosk"-License, as well as those using "MS365 Business Standard", "MS365 Business Basic" or "Exchange Online"-License.

[Mike Resseler]

All,

Please create support tickets if you are experiencing this issue.

Thanks
Mike