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

[ReKe]

Hi,

here are some new findings. Looks like MS has disabled EWS for Kiosk licenses. If you try to reanbale it with "Set-CASMailbox mailbox@domain.com -EwsEnabled true" MS returns an error that it is not possible for this license.

Greetings Rene

[aeph]

Got the same advice directly from veeam support - We have passed this information directly on to our customers.

Did Veeam support not try this beforehand? It is unprofessional for us to pass this information on to our customers and then have them report back to us that it doesn't work.

[nevakee]

I have the same issue since November 19.
However, only 7 shared mailboxes are affected. User mailboxes with an Exchange Online Plan 1 license or other shared mailboxes are not affected.

[aeph]

We created a test mailbox and assigned a MS Kiosk license. Tested the Set-CASMailbox test@mailbox.com -EwsEnabled true command and observed a error.

The error indicates that it is not permitted to activate EWS with this license.

We reported this to veeam.

[MiMaMo]

I have the same error message on 3 Mailboxes after the update to 8.2.0.2202 last friday. The affected Mailboxes have an E3-License attached regarding my colleague. I will now create a ticket for this issue.

[DaStivi]

i've doublechecked my affected mailboxes... these are all F1 Licenses... according to m365-maps its a "exchange calender" license... not found anything to this.. but F3 have the kiosk license..

according to microsoft "Exchange Online Kiosk" can't use EWS as stated in this table:
https://learn.microsoft.com/en-us/offic ... some-plans

not sure if this has changed, or was there allready and just not enforced?!