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NDR's from one domain, for only one user...

Hello Experts,

I have a couple nagging exchange issues. We are using Exchange 2003 on Windows Server 2003 (Enterprise Edition, and SP2). In the first case, we have one user within our domain that cannot send emails to one external domain. All of his messages get dropped into the queue on our exchange server and it keeps re-trying for 48 hours before he finally gets an NDR. Also, this is a remote user who uses VPN to connect to a workstation here in our office, at which time he will use Outlook like regular in-house employees, but also uses OWA quite a bit. He says it happens when he emails from either source.

The NDR says:

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

Subject:  XXXXXXX      
Sent:   2/3/2009 11:51 AM      

The following recipient(s) could not be reached:

  User@externaldomain.Com on 2/5/2009 12:02 PM
  Could not deliver the message in the time limit specified. Please retry or contact your administrator.
  <smtp.mydomain.com #4.4.7>


When I send an email to the same user, from my own domain account, it is delivered. I also sent one from my personal account and it worked, and he has been using his own personal account to communicate for the time being, so his is working too. The only issue seems to be with his domain account emailing this one domain. All of his emails to other domains are transmitting just fine.

I can telnet into the remote server but get the following errors when attempting to do anything:

 220 *******************************
helo
 502 unimplemented (#5.5.1)
ehlo
 502 unimplemented (#5.5.1)
HELO mydomain.com
 502 unimplemented (#5.5.1)
mail from: user@mydomain.com
 502 unimplemented (#5.5.1)

Now, this would appear, to my admittedly untrained eye, that the problem is on the recipients end. But I have spoken with their domain admin and she told me that everything on their end checks out as well. I am unsure where to go with this form here.

For the other issue, we have a different user who has a similar problem sending to one domain also...a totally different domain than the first one though. In that case, I can successfully transmit a message via telnet that the recipient has replied to. In this users case, he gets the NDR immediately and the message on that one is:

"The following recipient(s) could not be reached:

'User2@externaldomain2.com' on 2/9/2009 10:18 AM
There was an SMTP communication problem with the recipient's email
server. Please contact your system administrator.
<smtp.mydomain.com #5.5.0 smtp;554 Transaction failed>"

These cases seem to be related, which is why I asked them both in one thread. Maybe they are unrelated though and it was just a coincidence. Anyone have any ideas on either of these issues?

Thanks
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ITGonline
Asked:
ITGonline
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2 Solutions
 
lakshmidurgaCommented:
check whether the domain is blacklisted. use www.mxtoolbox.com 
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ITGonlineAuthor Commented:
Thanks for the suggestion, but I quickly ruled this out when I tested it by sending an email myself from the same domain. The only way I see this being the case is if the senders entire address got onto the recipients exchange server block list. Not sure if they use any kind of filtering on their end, but its possible that they have this one user blocked for some reason...but that still puts us at the mercy of their admin, who has said "everything is fine".
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lakshmidurgaCommented:
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ITGonlineAuthor Commented:
Thanks for the suggestion Lakshmidurga...

I still believe the issue was on the recipients end because the problem just went away after a few days, and we did nothing to fix it on our end. We are still monitoring the emails from this one user to this one domain, but apparently all is well now...at least for the first issue I mentioned. I will leave this open for a few more days while we monitor the situation, just in case, and to see if anyone has any other input.
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ITGonlineAuthor Commented:
This issue is still occurring. We believe that it is being caused by a feature called Mailguard on their firewall. Currently waiting for a good time for them to turn it off and run some tests, but thought I'd throw an update on here since its been a week and a half...
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