See Orasi Support Document - How to turn off e-mail notification when adding new users in Quality Center

If you can't get to that document mentioned, here is the answer

By Default email notifications are sent to the project administrators when new users are added and
removed from a project in Site Administrator.

AUTO_MAIL_USER_NOTIFICATION is an optional Site Configuration paramater to toggle the notification functionality on and off. This parameter enables you to prevent Quality Center sending automatic email notification to project administrators when users are assigned or removed from a project in Site Administration.

If this parameter is set to ''N'', then automatic notification is not sent to project administrators. If this parameter does not exist, is empty, or is set to ''Y'', then automatic notification is sent.

To disable automatic notification perform the steps below:

1. Login to the QC Site Administrator
2. Navigate to the Site Configuration Tab
3. Click the New Parameter Button
4. Enter AUTO_MAIL_USER_NOTIFICATION for the parameter field
5. Enter N for the value field