Problems with outgoing mail in exchange 2010 (DNS Issues)

We seem to be having big issues with e-mail going out from our exchange 2010 server...

Quite alot in the outgoing queue we're getting 451 4.4.0 DNS query failed
for example i just e-mailed someone at virtualvoiceservices.co.uk and it gave the above.

did nslookup
set type=mx

and it came back immediatly resolving the MX record....

I have set exchange to use external DNS for the external lookups....and ive put the google DNS server to do the lookups 8.8.8.8

Any idea's?



deepslalliAsked:
Who is Participating?
 
sunnyc7Commented:
Your DNS is clean as a whistle.

a) you use Google DNS as forwarders.
Can you try using your ISPs DNS instead of Google DNS
that will perform name resolutions faster.

TEST: Forwarders/Root hints (Forw)
                  Recursion is enabled
                  Forwarders Information:
                     8.8.8.8 (<name unavailable>) [Valid]
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Go to your Firewall / Router
Fetch ISP's DNS servers from there

From your DC

start > run > dnsmgmt.msc
Right click on server name > properties > forwarders
Enter your ISP's DNS there.
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I also noticed something interesting
It appears that your external and internal domain name's are same.
sscs.co.uk

Did you configure a split-brain DNS for name resolution ?

Please post back
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Muhammad MullaCommented:
Have you got DNS forwarding set up in your AD DNS server?
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deepslalliAuthor Commented:
Indeed we have Sir !

Forwarding is set to ....8.8.8.8

Cheers,
S
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mcsalladCommented:
We had the same on our end. I disabled forwarders and used the builtin root hints in our windows dns servers instead. Now all is well.
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deepslalliAuthor Commented:
Will give this a try then ! will report back !
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sunnyc7Commented:
I'd say - dont go for root-hints, rather go for ISP's DNS servers.
you will find the details in network connectivity section of  your firewall / router with public IP.

reason:
8.8.8.8 / Root-hints, they are couple of hops away and DNS resolution takes time.
ISP's DNS - 1 hop away = faster Name resolution.

--
run this from AD also

dcdiag /v /e /TEST:DNS > c:\dcdiag.txt

--
Also please increase the points :) - this is showing up as 50 points :(
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deepslalliAuthor Commented:
Here you go !,

Havent changed the DNS yet thought id show you what was happening on the dcdiag first :-)

250 points changed dude

dcdiag.txt
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sunnyc7Commented:
You will have to give me sometime to respond to this. I am stuck with a client issue :(

will reply.
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deepslalliAuthor Commented:
Done that, changed the DNS to 89.105.96.51 in the forwarders thats my ISP's DNS server

Should I run that command again to test the DNS?..

As for the sscs.co.uk unsure as I didnt configure it.....:/

Many thanks,
Shaun
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deepslalliAuthor Commented:
One thing i did notice in that log file was ..

 TEST: Forwarders/Root hints (Forw)
                  Recursion is enabled
                  Forwarders Information:
                     192.168.1.1 (<name unavailable>) [Valid]
                     192.168.1.2 (<name unavailable>) [Invalid (unreachable)]


Where would it be picking these 2 IP's up from ? as they do not exist on our network....
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sunnyc7Commented:
these are your local LAN IP

can you run the DNS test again
dcdiag /v /e /TEST:DNS > c:\dcdiag.txt
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deepslalliAuthor Commented:
Hiya,

We don't have any IP's of 192.168.1.1 / 192.168.1.2 though....we USED to have an ADSL router on .1 but not any longer...just worried something is trying to use them ....when they dont exist any more..

Here's the updated file

Many thanks,
Shaun
dcdiag3.txt
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sunnyc7Commented:
open IE
http://192.168.1.1

It might be the IP of your firewall / router
--
 Forwarders Information:
                     192.168.1.1 (<name unavailable>) [Valid]
                     192.168.1.2 (<name unavailable>) [Invalid (unreachable)]

---
These are IP's for local subnet. Preferably put the DNS for your public IP
Can you call up your ISP and verify the public DNS servers and put that there.

thanks


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deepslalliAuthor Commented:
Aha indeed it is the IP address of our ADSL router, but all traffic is sent straight to our CISCO asa on 192.168.1.254 , 192.168.1.1 is only just acting as an ADSL router...the DNS servers are .5 and .7

I can't find anywhere on the server where its showing 192.168.1.1 and 1.2 though...not in the network adaptor settings and not in the DNS settings....?
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sunnyc7Commented:
Go here
www.canyouseeme.org

Thats your Public IP.

Can you call up your ISP and tell them your IP and phone# and ask them what is the DNS server you are using.

--
You can also check in Cisco what is the DNS server being used there.

it has to be in the same subnet as your public IP (same / similar...)
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