Exchange 2007 Bounced MEssages

We have a customer running SBS2008 and Exchange2007.  Messages sent from one of their vendors are being bounced.  We have added the I.P. address to the IP Allow List but that did not allow the messages to be delivered.  The message size is small, 26kb.  The content is confirmation of a proposal.  The message is being sent in HTML format.  The I.P. range of the sender is 207.x.x.x.  The vendor also sends regular correspondence with an I.P. range of 74.x.x.x.  These messages are not bounced.

Any suggestions on other items to check will be appreciated.  Are there issues outside Exchange that can bounce a message?  
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Are you certain the message is being bounced by your server?  What's the NDR indicating?
barnettmnljsAuthor Commented:
They use Trend Micro's Hosted Email Security service with their e-mail.  Tracking logs with TMHES shows the message was received from the source, delivered to the Exchange server, and bounced.  

We have limited experience in Exchange.  How do I check NDR?

Thanks for your assistance.
NDR would be what you'd get if the message wasn't delivered.  It sounds like its being blocked by the exchange server somewhere.

What version of Exchange?  There is message filtering that can be enabled in exchange and perhaps that is where its getting blocked.
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barnettmnljsAuthor Commented:
They have Exchange 2007.  We have added the I.P. to the accepted list.  The other items we have checked are listed in our original request.  We believe the message is being bounced by a filter but have not been able to identify the source.  Any suggestions will be appreciated.
Is message tracking turned on?  That would be a good step in trying to track down the issue.  You could then see that the message is actually reaching the server, rather than taking Trend's word for it.
barnettmnljsAuthor Commented:
Message tracking is turned on.  The message is not listed in any of the catagories that can be checked.  We have tested with Windows firewall turned off but get same results.  We are considering turning off all the antispam to see if the message will be delivered.  If it is delivered, we can turn on the options one at a time to determine the stopper.  Should this work?  Will we need to stop and restart Exchange services between each change?
They use Trend Micro's Hosted Email Security service with their e-mail.  Tracking logs with TMHES shows the message was received from the source, delivered to the Exchange server, and bounced.
Sounds like Content Filtering is turned on and the SCL level is set a little high. You can find how to adjust the SCL here Adjusting the Spam Confidence Level Threshold.

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barnettmnljsAuthor Commented:
Based on our last submission, we were heading in this direction.  As a test, we disabled content filtering and the message was received.  Your suggestion provided a starting point.  We have re-enabled content filtering and will determine the right level of filtering.

Thanks to both of you for your suggestions and assistance.
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