To disable automatic forwarding:

  1. Sign in to the Google Admin console.
  2. From the dashboard, go to Apps > Google Apps > Gmail > Advanced settings.
  3. In the Organizations section, highlight your domain or the organizational unit for which you want to configure settings.
  4. In the Automatic Forwarding section, clear the check box Allow users to automatically forward email to another address.

It can take up to 30 minutes for the change to take effect.