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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.

Zachary Welch
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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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