Exchange Server 2013 DNS Issues

Hi Experts,

I have a server build as follows built for a small school with limited hardware:

1x Server 2012 running on physical server. Roles: AD, DNS, DHCP, WSUS, File Server.
1x VMWare server hosting an Exchange Server and a small Linux Box.
Both physical servers have adequate RAM and CPU and are new HP servers.

I have a problem with the exchange server. When the exchange server was built, there was an issue with the internet to the school so we proceeded without fully patching the server over the internet. After the internet link was fixed, we found that outbound mail was delayed but did deliver BUT inbound email was not bouncing with the error:

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

The KB article said this was an issue that Exchange 2013 Cumulative Update 6 could fix, however, sadly, after the CU6 update, all mailflow has stopped. I have checked with the configurations exchange server and everything is in place with accepted domains, email policy, DNS resolutions, Mail Routing using DNS and not Relay Server etc.. Late yesterday afternoon, I proceeded to point the exchange server to the google DNS servers to resolve Domain Names, after which a large number of exchange services failed. After a reboot, I was not able to log into the exchange server and authenticate to the AD. I am quite sure this is a bug, as I have built many exchange 2007 and 2010 exchange servers before and this is the first time I have come into this problem. Exchange is licensed (Standard) and so is the operating system (Server 2012 R2 Std).

Hope there is someone who can shed some light into this.
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Md. MojahidCommented:
Under Server configuration, right click on the Servername and select properties, under External DNS Lookups enter the external DNS servers IP addresses.

Then under Organisation Configuration > Hub Transport > Send Connector on the properties of your internet send connector under network check the box that says "Use the External DNS Lookup settings on the transport server" check box.

Restart the Microsoft Exchange Transport service
Mangi_PNGAuthor Commented:
Thanks Md. Mojahid. Currently the transport services refuse to start. Along with a whole lot of other Exchange services. Server has gone extremely slow. Any clues as to how I can get that sorted before I try your solution? As mentioned, this has happened after I changed the exchange server's DNS to and (Google Public DNS).

Appreciate the help.


Md. MojahidCommented:
Many places. Including the exchange 2013 system requirements page. Look at the "operating system" section and the big highlighted box that specifically calls out 2012 R2.
Simon Butler (Sembee)ConsultantCommented:
CU6 is already out of support. Therefore I would start by not wasting any more time with CU6, download CU8 and install that.

Ensure that the only DNS servers in the network configuration are the internal domain controller. No external DNS servers should be configured anywhere. While some will advocate using external DNS within Exchange itself, I have never found that necessary unless there are some odd restrictions on the DC being able to do external lookups.

If you are getting the error on outbound email, then I would suggest deleting and recreating the Send Connector.


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Mangi_PNGAuthor Commented:
Hi All,

So what happened was, every time I logged into the Exchange VM, it would be so slow and most Exchange services plus other network services on the server would not start up or would be forever idle is the starting point. This made it difficult to use the GUI to revert back to the DNS settings I had previously (i.e. pointing to internal DNS) before setting the it to lookup public DNS. I therefore used following steps:

1. Disconnected Virtual NIC (this improved responsiveness of server to allow me to work).
2. Used powershell to revert back to internal DNS and therefore remove external DNS settings. The reconnected vNIC.
3. Ran CU8 update. CU8 update could not resolve AD, so I ran ipconfig /flushdns to clear existing DNS Cache on the exchange server and re-ran CU8. CU8 was able to continue from its stopping point, then completed normally.
4. Rebooted server, but email was still delayed. I flushed DNS cache once more and checked all configs were in order.
5. Performed one more reboot and all emails started to flow normally again. Been monitoring for the past 4 days and all seems OK.

Thanks all for the help!
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