User email domain(s) can be whitelisted by Jira Administrator. Hence whitelisted users can only be added to Group(s) by Delegated user(s). This configuration can be done through Delegated Group Management > General Configuration.Either specific email domain(s) can be included or specific email domain(s) can be excluded by Jira/Confluence Administrator.
Image Modified
Now multiple users can be searched and added at once through modified 'Add user to group' screen.