I have a relatively new install of Exchange 2013 running on Server 2012. It has been up and running for about a month with no issues. I purchased and installed a cert from Godaddy about a month ago and installed it and, again everything was working fine. There are only 4 users. A couple of days ago it stopped working. All users upon opening Outlook or accessing their mail on their phones were asked the for the dreaded Windows Credentials”. Of course it does not matter what user and password you enter it does not connect. This includes the domain admin and password. When I went to look at the server I could not access the ECP. I had to go the IIS Manager, Default Site, and Bind both port 443 to the cert I installed from Godaddy. I can now access the ECP but I do not see anything unusual. All services are running. The event shows schannel errors. I have seen this before when there is a cert problem but this has been running for a month with no issues at all. Any help with this would be appreciated.