SMTP and POP3 RESTRICTION

[iovo]

hello
i want to make some restriction.
i've ISPConfig instaled and work very good, but i have some sequrity hole.
when i use php mail() from other server i can send e-mail!!!
here is php simple code:

ini_set("SMTP","hhh.hhh.hhh.hhh");
mail('hhhh@hhh.hhh', $subject, $message, $headers );

How can i restrict that!?
i've found somthing about this problem in internet, but i don't know that it is right:

smtpd_recipient_restrictions =
permit_mynetworks
check_client_access hash:/etc/postfix/client_access
reject_unauth_destination
if this work, how can i maket it work with ISPConfig installation

Thanks