At the start of a new session, Exchange Administrator re-connects to all the servers that were connected when you closed the last session.
You can alter the Connect to Server settings for an administrative workstation, but not globally for all administrators on all computers.
To prevent Exchange Administrator from trying to connect to a server at startup, select File.Close when the server name is displayed the Connect to Server drop-down box (left edge of the toolbar). This won't remove the server from the drop-down list.
To empty the list, run a single session of Exchange Administrator. Use File.Close for every server, until the workspace is blank. Then exit Exchange Administrator. Use Regedt32 to navigate to:
In the right hand pane, select the Servers value name and delete it.
NOTE: If you wish, you can simply edit the Servers data value to add or remove entries.
After you exit the registry editor, you can restart the Exchange Administrator.