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Some messages from a specific domain are never received by our Exchange 2010 server. No NDR on sending server.

The issue appears to be completely intermittent.  Some emails get through, some dont.  The disappearing messages contain attachments at times, and no attachment other times.  It appears that 'most of the time' the messages ARE received.  The fact that no NDR is received by sender makes it impossible for either party to know the email didn't go through.  This is causing a huge communication bottleneck during important projects.
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raduk
Asked:
raduk
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2 Solutions
 
Patrick BogersDatacenter platform engineer LindowsCommented:
Hi

Open ESM -> Toolbox-> Message tracking center and try to discover what exchange does with it. It should give you a clue.
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jrhelgesonCommented:
What anti-spam vendor are you using?  If it is randomly flagging/dropping messages as spam you will not get any NDR's.
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radukAuthor Commented:
Patrick,

The delivery reports do not show the messages ever touching our server.  I can see the messages in delivery reports when they are received successfully, they aren' there when we have the 'vanishing emails'
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radukAuthor Commented:
jrhelgeson,

Our ISP provides spam filtering using barracuda servers.  They then pass on the messages to us.  I find it odd that some messages would get through the barracuda filtering and other dont.  And the issue only appears to be with 1 particular domain.
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jrhelgesonCommented:
It's got to be the SPAM filter then.  Either your filter for incoming mail, or the senders filter for outgoing mail is cutting & silently dropping the message.
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Patrick BogersDatacenter platform engineer LindowsCommented:
Then it is possible a anti-spam software/hardware solution is doing the filtering/dropping for it reaches exchange. Is there something like GFI spam filtering installed on that box?
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radukAuthor Commented:
Patrick,

The only spam filtering we have is at the barracuda servers at the ISP.


jrhelgeson,

The ISP tends to not like taking responsibility for things.  I will contact them and see if they will 1. admit its their problem and 2. fix the issue.
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radukAuthor Commented:
Any suggestions as to what to tell the barracuda admins so they cant point the finger back at me?  Should I be checking smtp or receive connector logs in addition to the delivery reports in message tracking section of ESM?
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Patrick BogersDatacenter platform engineer LindowsCommented:
If you buy barracuda services from your ISP they should be able to whitelist that one problematic domain. Before you call the barracuda team make sure you have some solid info about the mail that is suspected being dropped. Info like:

What is the emailadress of the sender
When excactly was the mail send.
What is the subject for the mail
What is the emailadress of the reciever

With this info they can filter very fast.
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jrhelgesonCommented:
Spam filters keep logs of all messages they deliver, and all messages they drop. Ask the ISP to provide you a transaction report for your specific source/dest information.  Have them check the quarantine.
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radukAuthor Commented:
Turns out that the sending organization was using an email service that utilized multiple email servers.  2 of those email servers have been on blacklists for the past 6 months or so.  The barracuda server at our ISP was silently dropping emails coming from the blacklisted servers.  This explains why the problem was intermittent.  

You both were very helpful.  Thanks for your help.  I will split up the points between the two of you.
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