Hello Experts. In my staging environment, I have Exchange 2013 CU18, with AD 2012 R2, and using Outlook 2016. I am testing for implementing Outlook connections to use MAPI over HTTP with NTLM auth for our production environment. Currently, Outlook is using RPC over HTTP with NTLM. I have made the required changes on the exchange server, as they relate to the MAPI virtual directory, and made the required changes to our F5 load balancer through which traffic is flowing. However, Outlook is only able to connect via MAPI over HTTP using 'Negotiate' authentication. on the mapi virtual directory, if i choose for -IISAuthenticationMethods to accept only NTLM, and OAuth, Outlook keeps prompting for credentials, and it does not accept those credentials. so Outlook is not able to connect to on-prem exchange.
for the MAPI virtual directory, for -IISAuthenticationMethods, when i select 'Negotiate' aswell, then Outlook is able to connect via MAPI, without prompting for any credentials, but is using nego* auth to connect.
On the Exchange server itself, in IIS, for the MAPI default web site IIS authentication, i've enabled Windows authentication. Why is this happening?, why is NTLM auth not working? Thanks in advance.