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I have a (non-Exchange) mail server which works fine. But some people cannot send us emails when they use Exchange. We don't see any connection attempt to our mail server from their SMTP server. I think it may be a DNS problem, because we have a custom DNS server on our side (for the domain, but I have no Exchange server to debug the issue. Did someone already had this kind of problem ? Can someone try to send me an email on test 'at' from an Exchange server and, if it fails, track down all the delivery process ?

Here is a bounce message returned to a sender by Exchange :

Reporting-MTA: dns; 
Received-From-MTA: dns;
Arrival-Date: Mon, 23 Jan 2012 15:20:50 +0000 
Final-Recipient: rfc822;
Action: delayed Status: 4.4.7 
Diagnostic-Code: smtp;400 4.4.7 Message delayed 
Will-Retry-Until: Wed, 25 Jan 2012 16:20:50 +0100 

Thanks a lot !!

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up vote 0 down vote accepted

Problem solved : Exchange didn't like the DNS server on our side. We changed our DNS server to a basic Bind9 setup and now it's ok.

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Please remember that you can mark your own answer as the solution to your question. If you could add more details about your previous DNS server (that caused the issue) that could be helpful to other users with the same issue. – Oliver Salzburg Jan 31 '12 at 19:20

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