We have a new build Exchange 2016 server (on Server 2012 R2) and several Outlook 2016 clients. When we attempted to connect the clients with the default settings on Exchange (no SSL added, namespaces not changed etc.), apart from a certificate error which we could ok to continue, the clients connected properly.
Today, we added a GoDaddy SSL and changed all our namespaces to the external address e.g. office.domain.com. Now, the clients still give the certificate error but they also won't connect to Exchange with the error :
The action cannot be completed the connection to Microsoft exchange is unavailable outlook must be online or connected to complete this action.
We have an identical setup in two other offices (none are linked) and they work perfectly with the same settings. We have double checked their namespaces, DNS, IIS bindings and run Outlook test settings, but nothing will make these clients connect. The only difference is the faulty office is using Cumulative Update 2.
I'm slowly going insane here so would greatly appreciate any help to resolve this. I have tried rolling one client back to Office 2013 but get the same error.