Possible relationship between PHP Mailer and Mailer-Daemon

I am using the PHPMailer Class from a website which sends confirmation of the user ajax upload to my client. This uses the mail.myclient.com SMTP Host. This is the same SMTP Host that my client uses for his outlook to check his emails.

This email from the website gets sent without errors although I have received two emails from my client regarding Mail delivery failed: returning message to sender for the same address I have used to send confirmation emails out from.

Can these two issues be related? Do I need to provide more info?

Thanks a bunch!

   From: Mail Delivery System <Mailer-Daemon@hp13.hostpapa.com>
Date: Tue, 11 May 2010 15:01:41 +0100
To: "sales@splashoflondon.com" <sales@splashoflondon.com>
Subject: Mail delivery failed: returning message to sender

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:

  root@hp13.hostpapa.com
    (ultimately generated from Mailer-Daemon@hp13.hostpapa.com)
    retry timeout exceeded

------ This is a copy of the message, including all the headers. ------

Return-path: <sales@splashoflondon.com>
Received: from cpc2-dals2-0-0-cust1159.hari.cable.virginmedia.com
([82.35.76.136] helo=[192.168.2.7])
 by hp13.hostpapa.com with esmtpa (Exim 4.69)  (envelope-from <sales@splashoflondon.com>)  id 1OBq1k-0000V5-I4  for Mailer-Daemon@hp13.hostpapa.com; Tue, 11 May 2010 15:01:40 +0100
User-Agent: Microsoft-Entourage/12.0.0.071130
Date: Tue, 11 May 2010 15:01:31 +0100
Subject: Re: Warning: message 1O9xTC-0005BR-S6 delayed 48 hours
From: sales <sales@splashoflondon.com>
To: Mail Delivery System <Mailer-Daemon@hp1开发者_如何学编程3.hostpapa.com>
Message-ID: <C80F21CB.19D9%sales@splashoflondon.com>
Thread-Topic: Warning: message 1O9xTC-0005BR-S6 delayed 48 hours
Thread-Index: AcrxEnUcAvjUl38nTNq1kGDCVl/LEQ==
In-Reply-To: <E1OAgvb-0004TQ-Kq@hp13.hostpapa.com>
Mime-version: 1.0
Content-type: text/plain;
 charset="US-ASCII"
Content-transfer-encoding: 7bit

This is most likely harmless.

In the beginning, there was a warning E-Mail about a delayed transmission (probably one of the E-Mails your client sends out). A mail server could not be reached for 48 hours, maybe because it was down. (That is not an "undeliverable" report - the mail server will still try to send the mail out. If you hear nothing further, the message was eventually received.)

This warning was sent to root@hp13.hostpapa.com (for whatever reason I don't know, you'd have to check the outgoing E-Mails for that address. Do you have a specific errors-to header specified?)

The root address however, doesn't exist or doesn't accept mails, so an error message gets dispatched to the original sender.

It doesn't make 100% sense because it's not clear why root@hp13.hostpapa.com was contacted in the first place - maybe because hp13.hostpapa.com is the outgoing mailserver. As I said, try adding a errors-to: xyz@xyz.com and watch where such notifications end up in the future.

Anyway, the root of the cause looks harmless: It can happen (although it should be rare) that a recipient's mail server is down for 48 hours.