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The organization responsible for our mail infrastructure has recently embarked upon a migration to Microsoft Exchange. The group I work with has encountered some problems with the Exchange implementation. Because there are political issues involved here as well as the technical ones, I'm looking for a little help understanding how Exchange operates before I go to the IT folks.

Exchange is currently hosting the example.com subdomain. We have applications on hosts within this domain that expect to receive email directly. Due the local mail routing infrastructure, email from outside of our organization to, for example, user@machineA.example.com works just fine...but mail sent to the same address from within the Exchange environment bounces with the following error:

#554 5.4.4 SMTPSEND.DNS.NonExistentDomain; nonexistent domain ##

This happens regardless of whether or not there exists an MX record for the target host. It appears that Exchange believes that it is unilaterally responsible for both example.com and all subdomains thereof.

Is this fundamental to the behavior of Exchange? Is there a way to configure Exchange so that it Does The Right Thing according to RFC2821, even for subdomains of the domain for which it is the primary mailserver?

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My understanding of Exchange is that it wants to run the domain and everything under it but I do not speak from an authoritative position. In cases like this, I might consider a separate MTA which manages the domain and sub-domains, and let Exchange do the internal stuff only. –  user3914 Dec 10 '10 at 20:43
    
@larsks - Which version of Exchange are you using (I'm thinking 2007 or 2010 from that message)? Also, what's the tl;dr of that RFC .. I don't have the will to read it :) Sorry but you'll have to spell out exactly what your desired behaviour is for me. –  Ben Pilbrow Dec 10 '10 at 21:26
    
@Randolph: I would consider that, too, but unfortunately this wasn't my decision or responsibility. All we can do is hope to understand it :). –  larsks Dec 10 '10 at 21:31
    
@Ben: That would be the SMTP RFC, which I figure will be familiar to folks in a position to answer this question. –  larsks Dec 10 '10 at 21:40
    
@larsks - Unfortunately you figure wrong. I can go on for hours about Exchange (look at the top users for the various [exchange] tags), but to be perfectly honest I don't read through the RFCs. –  Ben Pilbrow Dec 10 '10 at 22:01
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up vote 2 down vote accepted

It looks like in our case the problem boils down to the fact that Active Directory is configured to be authoritative for DNS requests in the example.com domain, even though technically it shouldn't be...so the error message being returned is fundamentally accurate; AD doesn't know about hostA.example.com even though the resource record exists in the organization real authoritative nameservers. I guess we'll be taking this up with the AD folks.

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Good spot. I think if you accept your own answer, this will settle the matter. I've voted you up. –  user3914 Dec 10 '10 at 23:29
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