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Annoying bouncebacks with relay issues, urgent help is needed

Posted on 2006-11-21
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Last Modified: 2007-12-19
I have a customer who is sending out email to large amount of recipients, and is getting many bounce backs. I will paste all of the bounceback summaries below, with email addresses removed. Do note that ALL the email addresses used in these email are actual email addresses, and do exist on the mail server that they are on:


Your message did not reach some or all of the intended recipients.

       Subject:             ATTN CREDENTIAL HOLDERS: Re: Summit Pacific College President Appointment

      Sent:                 11/14/2006 12:49 PM



The following recipient(s) could not be reached:

      x@x.org  on 11/14/2006 12:49 PM

            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.

            <PAOC-Exchange.paoc.local #5.5.0 smtp;550-Relaying to 'gtonline.org' denied. If you are an Islandnet.com customer,>
 

The following recipient(s) could not be reached:

      x@x.ca  on 11/14/2006 12:50 PM

            The e-mail account does not exist at the organization this message was sent to.  Check the e-mail address, or contact the recipient directly to find out the correct address.

            <PAOC-Exchange.paoc.local #5.1.1 smtp;550 5.1.1 <x@x.ca> User unknown; rejecting>



The following recipient(s) could not be reached:

      x@x.org  on 11/14/2006 12:48 PM

            The e-mail account does not exist at the organization this message was sent to.  Check the e-mail address, or contact the recipient directly to find out the correct address.

            <PAOC-Exchange.paoc.local #5.1.1 smtp;550 5.1.1 <x@x.ca> User unknown; rejecting>


The following recipient(s) could not be reached:

      Jack Keys APA on 11/14/2006 12:50 PM

            The e-mail account does not exist at the organization this message was sent to.  Check the e-mail address, or contact the recipient directly to find out the correct address.

            <PAOC-Exchange.paoc.local #5.1.1 smtp;550 5.1.1 x@x.ca  User unknown; rejecting>


The following recipient(s) could not be reached:

      x@x.net  on 11/14/2006 12:47 PM

            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.

            <PAOC-Exchange.paoc.local #5.5.0 smtp;550 <x@x.net>: User unknown in local recipient table>

 

 

The following recipient(s) could not be reached:

 

      x@x.ca  on 11/14/2006 12:47 PM

            The message reached the recipient's e-mail system, but delivery was refused.  Attempt to resend the message.  If it still fails, contact your system administrator.

            <ES1.twu.ca #5.2.1>
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Question by:newgentechnologies
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by:susanzeigler
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I would guess that at least part of the issue is caused by one of two things. Either reverse DNS issues or your customer's domain is in a blacklist. Both of those can cause false user-unknown errors.

First, check the reverse DNS for the mail server your customer is using. At a command prompt type:
         nslookup xxx.xxx.xxx.xxx
         (where xxx.xxx.xxx.xxx is the public IP of the mail server they are sending through)
   See if it matches the host name in the MX record for the domain that they are sending through.

Blacklists are a bit more tricky--you can kill two birds with one stone and try the IP/hostname of the mail server here: http://www.dnsstuff.com/
That site will give you the reverse DNS as well.

Are any of the users that delivery is being refused for within the same domain as the sending server they are using? It also appears that the sending server is attempting to deliver locally but the mailbox aren't set up on that specific server and it doesn't know to forward them on.
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by:newgentechnologies
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The tests fail for both of those.

The domain in question is mail.bc.paoc.org. It is hosted by us as well as many other domains are hosted on the same machine. The ip for it is 64.40.105.233
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by:Hypercat (Deb)
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Most of those errors indicate a problem at the receiving mail server, not on your mail server.  I just did an nslookup on your domain.  Both your MX and PTR records are responding correctly from my end, so I don't see a problem there.  Occasionally, and more often lately, you will run into servers that are configured to reject emails that have more than a certain number of recipients listed.  I think the Exchange limit by default is around 100 or so, but it is configurable, so it's up to the sysadmin. So, if you're sending your emails out with large numbers of recipients in one email message, you might be running into this.

Hope this helps!

Deb
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by:susanzeigler
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Hmmm, not sure why DNSReport site is choking on your domain but that is moot for the moment.

Forward and reverse matches fine for your mail.bc.paoc.org server. There are two MX pointers for that domain. The higher-preferenced (i.e. preferred one) is for a different mail server (smtp.viewmymail.ca). On that one, reverse DNS does not match.

Which server is it that houses the mailboxes for the bc.paoc.org domain? Are the unknown user messages that the PAOC local server is reporting emails from within your own domain?

Which server is it that they are sending through and getting the unknown users for that domain? I suspectdomain is set up locally on both and both think they are to be receiving mail
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Sembee earned 500 total points
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The server concerned seems to suffer from an identity crisis.
If I telnet to mail.bc.paoc.org then it tells me its name is PAOC-Exchange.paoc.local
That will cause you problems.

Simon.
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by:newgentechnologies
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Well, that is the internal name of the server. Could you please elaborate how that would cause some problems.

Thanks Simon.
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by:susanzeigler
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If a sending host is not identifying itself correctly, mail can get caught in spam filters or rejected due to invalid information (i.e. the mail says it is coming from the bc.paoc.org domain, DNS says that the sending server is supposed to be mail.bc.paoc.org but your server insists it is PAOC-Exchange.paoc.local.

Since your domain is not in any blacklists, that is a likely cause for rejected messages. To fix it, you will need to set a Masquerade Name. This basically replaces your local host's name with the publically identified one in email headers.  

To correct that in either Exchange 2000 or 2003 follow steps at the following link:
 http://support.microsoft.com/default.aspx?scid=kb;en-us;314331&sd=tech

That could be the cause of rejected messages.

As to the messages that are destined for the local domain and that are getting unknown user errors, we still need to find out whether the mailboxes are actually hosted on the Exchange server or if they are hosted at the other server listed in the MX records (or a separate server that isn't even listed).
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by:Sembee
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Put the domain in to dnsreport.com - it will show you what happens when your server announces itself incorrectly.

Simon.
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by:newgentechnologies
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Thanks for the input.

Susan, the local domain ones are mailboxes hosted on a seperate Exchange server. the domain in question is myapa.ca.

Turns out there is a faulty mx record in the DNS settings for bc.paoc.org, width higher priority than the proper MX record that is also there. I am guessing this will cause lots of problems.

I have setup the masquarade domain, as bc.paoc.org, I feel it should be fine now. What can I do to test?
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by:newgentechnologies
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On a side note, do any of you know a free IMAP server migration tool? Looking to take a number of mailboxes on one IMAP server, and move them to another.
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by:susanzeigler
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In addition to the masquerade domain name, on that same tab you should enter the FQDN (Fully-Qualified Domain Name) of the host which should be mail.bc.paoc.org--I didn't say that before, but I should have.

You will want to stop and start the SMTP service after you add in FQDN of the host name.

If you have an external email address, you can try sending to that and looking at the header to see if the information is updated. If the FQDN is updated correctly, the server should respond with mail.bc.paoc.org when you telnet in on port 25. To do that, simply go to a command window and type:
telnet mail.bc.paoc.org 25

It should answer and respond with its name.
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by:newgentechnologies
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Thanks Susan.

For now I will leave all that be though. I think the problem is related to A: An additional MX record with a lower weight beind in the DNS, which is invalid in the first place; and B: The user who is getting these bouncebacks is sending the mail to over 700 recipients. Far too much I would think for most mail servers to not mark it as spam.
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