Uh you cant? Unless you have access to the domains e-mail addressbook.. or all the known mailboxes... If such an option existed, it would make it really easy for spammers..
If you use dovecot, you can list users (not aliases) with 'doveadm user -u @test.com'. You must have iterate_query set (which is already done by default on recent ispconfig versions). Or you can go right to mysql and look in mail_user and mail_forwarding tables. Or you could look up that info via the ISPconfig remote api, if that's a better fit.
ok i am the maintainer of this email domain where i can easily do these steps you mention above to get all the known address ... but i thought in ispconfig 3 panel you can do this ... anyway thanks for all your help