DNS flushing is it OK?

[jeremy mendoza]

Guys,
If I flush my DNS server (and it is integrated with AD, and it is also my DC!!!) would my problem with sending email from some recipients would be addressed? Or is it ok to delete DNS role and then installing it again?
System:
Win 2k3 Std with SP1
Exchange 2k3 with SP1

regards,

JM

[Jonathan Axford]

Hi JM,

If it is just a few people you are having toruble sending e-mail from then it probably won;t be the server that ats fault.

YOu can flush the DNS cache on the server without causing any trouble by using the following froma command prompt:

ipconfig /flushdns

If you take DNS off of the DC and re-install it, you will definately effect everything, especially if it is your only DNS server.

What are the actual problems you are having?

[jeremy mendoza]

Jonathan,

Hi! thanks for the reply.. you see from our company email-we can't send and I mean we really can't send any email to some of our clients (preferably aim.com, aol.com)... So do you think its a Dns problem of our server?
P.S.
I'll keep in mind about the NOT to reinstall DNS.. (Scary.!!! :{)

regards,

JM

[Jonathan Axford]

Hi JM,

Is it possible that your Domain name is blacklisted? This will stop you sending e-mails to certain companies...

Can you send e-mails to places like Hotmail.com etc?

Also, can you browse the internet from inside your network? This relies on the same DNS process that the Exchange server uses to look up mail recipients domains, so if that works ok then DNS is not the problem.

Are you getting any Non-Delivery reports when you try and send mail to aol.com etc? Or is it failing at the Exchange server? (Can you see the mail in the queues?)

[jeremy mendoza]

Richard,

The answer is Yes! I can send to hotmail. and yes again aim.com its in the queue its been hours... and it sends to NDR if doesn't reach the recipients.



JM

[Jonathan Axford]

Hi,

What does the NDR say? By the sounds of it the problem lies with maybe an Anti-Spam device at the recipients end or maybe even your domain reputation.

A company i worked for once before got blacklisted incorrectly and we couldn't send any mail to aol.com.

One thing to test is whether you can send mail to the AIM.com address from hotmail, to make sure the recipient address is correct etc...

[jeremy mendoza]

Richard,

I can send mail from my yahoo, Hotmail to my aim.com/aol.com account. about being denied maybe it is... checked from dnsstuff.com, but what my isp told me that host our web and email there's no problem with their end. (Our Public IP and their Ip are the same.. Ryt?) I told the techie they are to send a mail to my aim.com account... as to my surprise, I received his mail! (Yaiks!).. frustrating isn't it?! > So what could be the problem? does it mean our server sucks bad? misconfigured exchange??? DNS??? But if it is miscon.. All of the incoming and outgoing mail should be affected. ryt? I can't think enemur... (It kills me...)

Waaaahhh

regards,

JM

[Jonathan Axford]

Do you host your own external DNS or does your ISP do this for you?

Also, you obviously send mail straight out from your Exchange server. Some companies Anti-Spam appliances run a check on the incoming SMTP connection to make sure the sending server is legitimate. This usually involves checking the EHLO/HELO greeting is valid and/or running a reverse DNS lookup on your IP address to make sure you have a Valid MX/A record.

It is worth checking that this is all ok, it would usually tell you in a DNS stuff lookup on your own domain if there are any issues...

[jeremy mendoza]

Jonathan, (sorry for the Richard.. hehehe)

Nope, our ISP does this for us. Actually this is the setup our exchange server 2k3 which is also a DC,AD has its static IP because for our OWA and at the same time for sending mail.. Is this wrong?

JM

[Jonathan Axford]

That set up should be fine.

Do the following:

Run your domain name through DNSStuff.com and look for any Warnings or errors

If there are, contact your ISP and ask them to address these errors.

If you want to give me your domain name i will take a look for you if you like.

[jeremy mendoza]

Here it is cimtechnologies.com thank you for giving time on this. thank you thank you.. (If we've addressed this problem you'll definitely earn my perfect vote!) Thanks again.. Peace!

JM

[Jonathan Axford]

Hi Jeremy,

It all looks ok from here. The DNSReport has come out ok.

The only thing that might be causing problems is your MX record, which is called

cimtechnologies.com

A receiving mailserver may see this as your server not having a hostname...

Does your DC/Exchange box have a hostname like DC.cimtechnologies.com? If so, that might be causing some Anti-Spam devices a problem as you will be sending mail from DC.cimtechnologies.com and when the receiving server checks this, it just gets cimtechnologies.com back from the DNS lookup...

No problems for helping out! Is what these forums are here for! (And some points wouldn't go amiss, i am only 13 points off 250!)

If you can get an NDR from one of the failures we can probably identify what is causing the problems

[jeremy mendoza]

jonathan,

Yup I agree to that! Congrats! I'll give to you the 13 points... I have a question about DC.cimtechnologies.com DC = domain controller ryt? what should i place there, if Im not wrong it is the netbios name of the server ryt???

what should i put in the FQDN? servername.cimtechnologies.com or mail.cimtechnologies.com?

What could be the right one? But one things for sure I've tried both of them and they are all valid FQDN... (Am I goin' nuts?!?!)

By the way here's my assigned points for you
JM

[Jonathan Axford]

Your server should have a hostname of your choosing.

It can be anything you like, the FQDN then becomes [servername].cimtechnologies.com

The MX record that comes up for your domain has the FQDN of cimtechnologies.com, so the hostname is cimtechnologies.

What is the server called, the DNS name and NetBIOS name are usually the same. So if the server is called 'Server1' the NetBIOS name would be SERVER1 and the FQDN would be Server1.cimtechnologies.com

[jeremy mendoza]

thanks man! Congrats again by the way!

So bottomline I really have to flush the dns and clear the cache ryt? I'll post here again with the development..

Stay stuck!
Thanks again!

JM

[jeremy mendoza]

Hi,

I did flushed the dns..and clear the cache but still to no avail. I've found out about SPF! we don't have SPF in our domain that's why maybe the REASON why we can't send mail to some domains (D*mn!)... Do you know how to set this up?!

Peace!


JM