I seeing issues where users that have been upgraded from Outlook 2010 to Outlook 2016 are getting prompted for credentials when attempted to connect to the Exchange 2010 server. After entering username and password Outlook comes up fine. Looking at the Outlook Connection Status it's getting hung up when connecting to one of the mailbox servers (in a DAG) for the Exchange Public Folders. It doesn't happen on a consistent basis. Sometimes they get connected without a hitch. The CAS/HUB servers are set up as a CAA using Windows NLB.
I did some Googling and found references similar but it mostly involved occurring after migrations from Exchange 2010 to Exchange 2013. The most common resolution involved going into IIS and changing the authentication settings for EWS and Autodiscover each to disable Anonymous Authentication and then under the Advanced Settings for Windows Authentication, enable Kernel-mode authentication. Then restart IIS. I couldn't find anything specific about problems after upgrading from Outlook 2010 to Outlook 2016 and connecting to Exchange 2010. Besides the prompting everything is working fine and worked fine with the old Outlook. I'm looking for a bit of understanding why this started happening and the feasibility of the above suggestion correcting the problem. One concern is disabling the Anonymous Authentication. The other is that apparently the Kernel-mode authentication is enabled by default - which tells me someone disabled it. I'm not sure why someone would have done that other than a reference I found where sometimes Kerberos authentication fails when you have kernel mode authentication enabled. Does someone have a possible explaination? Paul
