If you’re having issues removing an existing domain from Exchange due to the error in the title, try the following:
- On your Domain Controller, open ADSI Edit
- Select “Action” in the top bar
- Select “Connect To…”

- In the new window, in the dropdown box named “Select a well known Naming
- Context” and select “Configuration” Click “OK” on the Connection Settings window
- Double click on the new tree in the left side-pane to expand Navigate through this tree as follows:
CN=Configuration,DC=Company,DC=local >
CN=Services >
CN=Microsoft Exchange >
CN=COMPANY >
CN=Recipient Policies - Double click on CN=Default Policy to edit
- Scroll through the new window “Attribute Editor” until you find “gatewayProxy”
- Edit the gatewayProxy to remove the offending domain name.
Hopefully that helps you, if not, god speed.