<?php

    $date = date('y-m-d');
    $hostname = '';
    $username = '';
    $password = '';

    $inbox = imap_open($hostname,$username,$password) or die('Cannot
    connect to mailbox: ' . imap_last_error());
    $emails = imap_search($inbox,'SUBJECT "Undelivered Mail Returned to Sender" ON "'.$date.'"');


    if($emails){
    rsort($emails);
        foreach($emails as $email){
            $overview = imap_fetch_overview($inbox,$email,0);
            $message = imap_body($inbox, $email);
            print_r($overview);
            print_r($message);
            echo '<br>';

            print_r($email);
        }
    }