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I don't know how to title this question as it's a very odd situation.

I have a corp domain with it's PDC/BDC and DNS on corp.thisdomain.com in a datacenter. It also has a cloud hosted email server at mail.thisdomain.com.

The issue is that internally all clients need to resolve to the actual internal IP address of mail.thisdomain.com server, but instead via the PDC/DNS are going outside the network first, then resolving to mail.thisdomain.com external address. This is creating a loop back of all traffic and affecting performance.

Is there a way in windows DNS to create an exception for a higher level request? Considering that in the domain hierarchy ., com, thisdomain, would be above the corp.thisdomain.com domain used on the PDC for the internal network. Very curious problem and I can't seem to find a working solution.

Thus far I've tried a manual root hint entry, and an alias of "mail.thisdomain.com.corp.thisdomain.com" which works for nslookup, but ping tests still show the external address.

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Do you literally have an NT PDC, or do you just mean Domain Controllers? –  Dan Apr 5 '13 at 20:05
    
Is the mail server external? If it is then it doesn't matter what you do with DNS. All the traffic to the mail server will go out to the internet anyway. I'm failing to see how the DNS queries are creating a performance issue. How is it that the email server is cloud hosted but has an internal DNS record? –  joeqwerty Apr 5 '13 at 20:36
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You really need to get rid of those NT 4.0 boxes. –  Michael Hampton Apr 5 '13 at 20:52
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1 Answer

This isn't a trick, you simply need to configure split DNS - provide a different DNS server for internal and external clients, therefore providing different results as required.

The easiest way would be to create a new DNS zone called mail.thisdomain.com and create an empty A record with the internal IP.

I've written a couple of answers previously which should get you started:

Can we put random entries on DNS

Different Routes For The Same DNS

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