globalize your variables first:
<?php
class mailbox {
function openbox($host, $user, $pass) {
GLOBAL $host, $user, $pass;
setCookie('hoster', $host);
setCookie('usern', $user);
setCookie('passw', $pass);
$mbox = imap_open("{$hoster:110/pop3}", $usern, $passw);
}
}
?>