I'm utterly baffled by this, largely because until this morning, everything was working fine. I'm not aware of any changes that would explain this, though obviously something has changed, because none of our users can connect to Exchange (2013, Version 15.0
Build 1156.6, in a 2-server DAG) via Outlook 2016 (don't have any older versions of Outlook to test -- all users are updated automatically via Office 365). All are being told to enter a username and password, which are never accepted. I'm the Exchange
admin, so this is my responsibility to fix.
Users have no problem connecting to Exchange and logging in and getting mail via other paths. For example, I can get e-mail on my Windows Phone, in Windows 10 Mail, and via OWA. To test, I have restarted client and server computers, reset user
passwords, rebooted the AD servers, deleted and tried creating a whole new mail profile on one of the client computers, and deleted and recreated the connection to the server on Windows 10 Mail. Everything works fine everywhere except Outlook. After deleting
the mail profile, I can't recreate it to even launch Outlook, because it gets stuck on the username password window.
I also tried connecting Outlook to Exchange off the LAN, and they suffer the same exact problem, so it's not just the LAN side of the Exchange-Outlook connection that's failing.
Based on the symptoms, and that it affected all copies of Outlook at the same time, I assume this must be an Exchange setting. What could it be? Something to do with Autodiscover?
Unlike previous versions of Outlook, Outlook 2016 doesn't seem to allow me to manually enter the server name, AD domain name, and other information, so if it's not getting it right via autodiscover, I'm not sure how to troubleshoot or work around that.
The closet to changing anything that I can think of is that yesterday (mail was still working until this morning) I had disabled NTLM connectivity on the AD via Group Policy, but as part of debugging, I've since reverted that to the prior setting. I have
restarted all servers and the test clients since making that change back, just in case.
I don't think this is related, but one possible unusual aspect to our system is that our OWA domain name is remote.ourcompanydomain.com and mail addresses areuser@marketingname.com. Note that they are different domains (ourcompanydomain vs. marketingname), and where our AD domain would be ourcompanydomain.local (same name as the OWA domain, but ending in .local and note
.com). To enter users we are (and always have) entering ourcompanydomain\user.
Colin