how to set email failed delivery message in box using php

Question

if (empty ($returnpath_name)) {
 $this->xheaders['Return-Path'] = $returnpath_email;
} else {
 $this->xheaders['Return-Path'] = "\"$returnpath_name\" <$returnpath_email>";

}
===========================
function Send ($ret) {
 $this->BuildMail ();
 $strTo = implode (", ", $this->sendto);
 re

turn mail ($strTo, $this->xheaders['Subject'], $this->fullBody, $this->headers,"-f $ret");
}

//This Program return failed delivery message in spam folder(yahoo and gmail) //please help