Unfortunately, the email parameters used in Site Admin will only accept one email address. If the parameters are used, then the email address specified will always display in the emails received. If you would like the email to show that it was from the user who made the changes to a defect, you will need to remove any parameters from the 'Site Configuration' tab in Site Admin that are used for the Automail feature, as this value will always display in the email regardless of who made the changes to the defect. After removing the automail parameter(s) from Site Admin, you will need to configure 'Automail' in Customization, selecting the defect fields that will trigger an email if any changes are made to them. I tested this in my environment, and the email received always displayed the users email address in the 'From' field who had made the changes to the defect.