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Email being blocked

Posted on 2011-03-25
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Last Modified: 2012-05-11
I have a very unusual email issue.  I have users who are sending emails to multiple domains but the recipients are saying they are not getting them.  The mail server logs are saying the email is being delivered to the destination servers.  In addition to this weirdness, I have one user who sends an email from his outlook client to a certain email address and gets an immediate bounceback with a denied message.  But, if he sends it from OWA, it gets delivered to the destination mail server.
I have checked all blacklists.  I have conected destination mail server administrators and we are not on internal blacklists, from what I can tell.  

Now, they did have an email virus on the network last week that sent out several emails.  But it was cleaned.
I am thinking that the virus may have marked the sending folks emails as spam on the clients.
Any thoughts ideas or ideas would help.  
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Question by:itarrows
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Expert Comment

by:mmicha
ID: 35216662
Are you natively sending mail through Exchange?  Possibly using a smarthost or outbound scanning?  Maybe something outside of Exchange blocking.  Spam Filter on your end (outbound) or filter on the other side of the fence.  

Is it only to certain domains?
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Author Comment

by:itarrows
ID: 35216685
We were using Exchange Defender as a smart host.  But, I am now sending directly out of exchange for outbound and by-passing the smarthost.  Also, the SMTP logs say it is being delivered to the destination mail server successfully.
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Expert Comment

by:mmicha
ID: 35216799
It's only to specific domains?  If you tested email flow to say hotmail or something it would work fine?

I'm thinking if Exchange says the mail is getting through it completely and leaving out the send connector is a foreign thing causing issue.

Does the deny message include any header information that may give clues?
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Expert Comment

by:Neil Russell
ID: 35216823
Have you enabled verobose SMTP logging so that you can see a full transaction conversation with a remote server connection?

IF You get an imeadiate bounce in Outlook client, do a few things.....
firstly delete the useres .NK2 file

Second make sure that the user has NO contact record for the user he is trying tosend too in ANY address book.
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Author Comment

by:itarrows
ID: 35216830
Neilsr, that's a good idea.  Let me look into that.
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Author Comment

by:itarrows
ID: 35217960
Has anyone heard of fingerprinting emails with neetwork solutions.
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Expert Comment

by:mmicha
ID: 35218759
I've not heard of it...  Is that what you think is causing the bouncing and non delivery?
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Accepted Solution

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itarrows earned 0 total points
ID: 35386915
The issue was that, certain domains had us marked as sending SPAM, which we had a virus last week, but had cleaned it.  But, the receiving domains (mostly hosted with mxlogic.com) had us flagged, if emails came in with a certain signature tied to it.  This is why emails witthout a signature, went through fine, but emails with the signature got dumped at the receiving site.  We had to contact them and ask them to remove the flag.
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Author Closing Comment

by:itarrows
ID: 35414427
I found this out working with network solutions and their new way to fight SPAM.
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