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Hello,
I have two Windows machines in the network on which Outlook (version 2201, build 14827.20198) tries to authenticate to Exchange 2016 CU22 /OAB (offline address book download) using NTLM and fails (error 401). The remaining 53 machines authenticate using Kerberos and succeed. All machines receive the same config by GPO and are in the same network segment. The two mentioned clients successfully connect to mailbox using Kerberos authentication.
In windows event logs on Exchange servers there are Event ID 4625 errors. In HTTPS logs I can see the following requests (authorization token edited) from the two clients:
{} "HEAD /OAB/6d1b7286-2670-4b61-9460-61a0092772f2/oab.xml HTTP/1.1"
{Negotiate TlR...} "HEAD /OAB/6d1b7286-2670-4b61-9460-61a0092772f2/oab.xml HTTP/1.1"
{Negotiate TlR......} "HEAD /OAB/6d1b7286-2670-4b61-9460-61a0092772f2/oab.xml HTTP/1.1"
{} "HEAD /OAB/6d1b7286-2670-4b61-9460-61a0092772f2/oab.xml HTTP/1.1"
{NTLM TlR...} "HEAD /OAB/6d1b7286-2670-4b61-9460-61a0092772f2/oab.xml HTTP/1.1"
{NTLM TlR......} "HEAD /OAB/6d1b7286-2670-4b61-9460-61a0092772f2/oab.xml HTTP/1.1"
The above requests receive a 401 response.
I welcome suggestions on how to find the cause Outlook tries to use NTLM for OAB download.
Kind regards,
Gregor
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Do they have some Outlook add-ins?
And if you create a new Outlook profile and configure another mailbox on these affected device, would the issue persist?
Hello @Kael Yao-MSFT ,
thank you. They do not have any Outlook add-ins. The issue was resolved after recreating the Outlook profiles.
Kind regards,
Gregor
Hi,
Thanks for the sharing.
Glad to hear the issue has been resolved!