title: Unable to receive sendmail bounce mails using php mail()
body: <p>I'm using the php <code>mail()</code> function to send mails to recipients</p>
  
  <pre><code>$to = "recipient@example.com"; 
  $subject = "Subject";
  $message = "This is a message from our website to say thank you";
  $headers = "From: sender@example.com \r\nReply-To: sender@example.com\r\nReturn-Path: sender@example.com\r\n";
  $additional = "-rsender@example.com"; 
  //(have also tried -fsender@example.com in $additional)
  
  mail($to, $subject, $message, $headers,$additional); 
  </code></pre>
  
  <p>It didn't send the bounced mail to sender@example.com. I checked the log (<code>/var/mail/mail.log</code>) and could find the below </p>
  
  <blockquote>
    <p>Jul  8 15:38:21 aspire680 sendmail[15850]: p68A8Lpl015850: to=recipient@example.com, ctladdr=sender@example.com (33/33), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30279, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (p68A8LVH015852 Message accepted for delivery)<br/></p>
    
    <p>Jul  8 15:38:21 aspire680 sm-mta[15854]: p68A8LVH015852: to=, delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=120589, relay=mail.aspiresys.com. [192.168.0.3], dsn=5.1.1, stat=User unknown<br/></p>
    
    <p>Jul  8 15:38:22 aspire680 sm-mta[15854]: p68A8LVH015852: p68A8MVH015854: DSN: User unknown<br/>
    Jul  8 15:38:22 aspire680 sm-mta[15854]: p68A8MVH015854: to=, <br/>delay=00:00:00, xdelay=00:00:00, mailer=esmtp, pri=30000, relay=mail.aspiresys.com. [192.168.0.3], dsn=5.1.1, stat=User unknown<br/>
    Jul  8 15:38:22 aspire680 sm-mta[15854]: p68A8MVH015854: p68A8MVI015854: return to sender: User unknown<br/>
    Jul  8 15:38:22 aspire680 sm-mta[15854]: p68A8MVI015854: to=root, delay=00:00:00, xdelay=00:00:00, mailer=local, pri=30000, dsn=2.0.0, stat=Sent<br/></p>
  </blockquote>
  
  <p>which clearly suggests it has sent the bounce mail to <code>sender@example.com</code> since <code>recipient@example.com</code> doesn't exist but I didn't receive any mail. Am I missing something here or what could be the problem. Please advice.</p>