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No such domain at this location

I am at a loss on this one I've tried everything that I can think of so hopefully someone will be able to assist.

We are running Exchange 2003 we also have a Barracuda Spam Firewall.  During the weekend (of course) we had a power spike, while everything appeared to be ok something went wrong with our email system as we are not able to send mail outside of our network anymore.  We are receiving mail just fine from all domains, but we cannot reply back to them.

This is the error we are getting:

t*****@gmail.com on 10/27/2008 12:44 PM
            There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            <EMAILSERVER #5.5.0 smtp;550 No such domain at this location (t*****@gmail.com)>

On the Barracuda the message log just gives a Invalid Domain error as the reason.

Steps I've taken:

I have reconfigured our firewall and bypassed the Barracuda sending all mail directly to the mailserver.
 --This was successful we were able to send mail out but we got a very excessive amount of spam

Deleted and rebuilt the SMTP Connecter in Exchange 2003 setting up the Smart Host ensuring it's pointing to the Barracuda

Verified all settings with Barracuda to ensure that the Spam Firewall was configured correctly (my gut tells me that they missed something though due to the fact we can send out when we bypass the Spam Filter)
  --We added the domains that send out from our mail server to the trusted domains
  --Added the internal mail server IP address to Trusted IP's
  --Mail is showing up on the message log on the Spam filter just not going anywhere after that.

I hope there is enough information here...logically it looks like the Barracuda is at fault, however maybe my brain is fried from looking at it trying to resolve the issue.  Any help or suggestions would be greatly appreciated.

Thanks!
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pit1140
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can you try so exchange the antispam gateway? e.g. virtual machine, maybe debian with exim? so you may test firewall and your exchange to be allright - to be sure.
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HMSTN

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I would check:
- which DNS are used in Barracuda to resolve domain names? If it is pointing back to your local DNS, make sure, your DNS is configured with forwarders
- try sending mail to somebody inside your local domain. If this goes thru, DNS might be guilty.
- is Barracuda connected to some Router? If it is Cisco router, you might have done some changes long ago, but you only APPLIED settings, and did not actually SAVE them to Router's NVRAM. Your unsaved configuration, which was active all the time until power-off, might be lost. Check Router's config, if port 25 is opened for Barracuda's IP.

Aren't you paying to Barracuda updates & support? I suggest you contact them, they will know where to look for trouble.
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HMSTN

I agree, I meant to say that earlier about the Barracuda support because you should be paying for that.
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HMSTN, you are right...that was really quite a dumb setup we don't need our outgoing going through the spam filter.  

I ran a test after reconfiguring and the mail did go through, still can't figure out why after 2 years it worked then died after a power spike...but if email is working then that's all i'm going to worry about.  I really appreciate your help thank you very much.

Also, we have been running our barracuda for 2 years now this is actually the first issue we have come across...I'll look into the AppRiver solution that you mentioned, I'm always looking for a better solution
Glad to hear that is working.  Yes I would at least take a look into AppRiver.  It works very nice and we have little problems out of it.  Glad I could help out.
we also had this exact same problem and found a fix to be enabling SMTP authentication on the client.