To begin, go to http://admgr.liebertpub.com.  Click the Options button on the bottom right of your screen:

Next, click on the Click here to configure the various ad zones link:

Next, click the pencil icon for the property you wish to edit the users for:

Next to the user's name, you will also see a second drop down box for notifications. Choose To, Cc or Bcc for notifications or leave this drop down blank if the user doesn't need to receive them. You do not need to hit the save button. Selections are auto-saved.