Recently we decommissioned one of our Exchange Servers. The server exchange server was a unified messaging role server. Being a unified messaging server, we never imagined running into issues. However a few days later we found ourselves faced with a situation where some of support staff unable to open the exchange management console hosted on our citrix servers. In fact the console was opening and was trying to connect to a remote exchange CAS server.  As we know when you open Exchange Management Console, it will generally connect to an Exchange CAS server in the same AD site. The error displayed is indicated shown below