We have an exchange 2010 environment, that we will run in co-existence with Exchange 2016. Today I installed Exchange 2016 but I didn't configure anything yet, no DNS changes, Names space changes or anything. All I did was install Exchange 2016. Today a user got a prompt about that 2016 server saying "The certificate was issued by a company you have chosen not to trust. View the certificate to determine whether you want to trust the certifying authority", I know this is because this is a self signed cert and I haven't imported any certs yet. But the question is why did the user's outlook attempt to connect to that server instead of the Exchange 2010 casarray? I have powered the server off for now, but curious as t why this happened.