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Error 501 - Invalid Domain

Posted on 2004-04-08
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Last Modified: 2006-11-17
Email is suddenly being bounced by our Exchange 2003 server, the senders getting the message 'Error 501 - Invalid Domain', and I can see the messages being stopped at our firewall.

The Exch 2003 server co-existed with a 5.5 box for 2 weeks and last weekend the 5.5 box was finally removed from the domain.  The 5.5 box was called oldbox and the new one is newbox.  A problem with OWA showed that the routing table in our router still showed 'oldbox' - our service provider changed it to 'newbox' yesterday and made sure it pointed to the right internal IP address.

Since then we have had no external email delivered.  We can send out no problem.  I've run checks on www.dnsreport.com and it shows everything works right up to it gets to the IP address of our firewall and then it says 'Invalid Domain'.  Our external address is outside.org.uk while our internal domain is inside.local.com. Our service provider says the problem isn't down to them, they're delivering the traffic to us, we're not accepting it.  

Any help in diagnosing and fixing will be greatly appreciated.

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Question by:swaman
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by:waybadmojo
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Make sure that your SMTP service is configured to answer up to outside.org.uk otherwise when a sending mail server talks to your box it will respond back with the wrong domain name.

-Mojo
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by:guitrain
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This is similar to the problem we are having only with a few domains though, and they cant send to us.
 I'll be following this one.
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by:swaman
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It's now solved but it was a bit complex, it was all to do with with DNS.

The Exchange configuration was ok, I could telnet into the server and access it using OWA.  A call to our firewall vendor led to us going through its config.  One setting was for email to be compared against an MX record and this was on.  Once it was turned off, the mail started to flow.

This is the reason: our Service provider had changed its DNS records to show our new Exchange server name.  However, we don't use our service providers DNS server for resolution, we use a totally different company, and it was this server causing the problems.  Email was trying to resolve against it and of course its MX record only showed our old Exchange server name.  Making the MX change in the firewall meant that mail no longer tried to resolve against it.  

Hope that makes sense, it's what the firewall tech told me - main thing is email is flowing and my users are all happy again.

Pauly






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