Two Exchange2003, same Domain, same Exc Org. Internal mail routing fails when outbound Smart Host is used
[I have a good diagram but cannot find any way to attach it. It is only a local JPG,...it is not "on the internet".] We have a Client with 2 Exchange2003 boxes. It is a single Mail Domain, single AD Domain, with a single Exchange Organization. Straight forward, simple, no surprises. First Exchange is the Bridgehead and is the only one that interacts with the firewall and internet. The second Exchange sits passively by and receives mail from the bridgehead or passe mail to the bridgehead if it is destined for the bridgehead Exchange or destined for the Internet. It works fine "as it is". However we now need to use the 3rd party SPAM Filtering Service for outbound mail as well,...previously was only filtering inbound. But as soon as I set the 3rd Party Service as a "smart host" on the bridgehead Exchange all of the internal mail routing fails. The Bridgehead Exchange ends up taking the internal mail that should be passed to the Second Exchange and instead sends it to the 3rd Party system,...who then does an MX lookup and sends it right back to the Bridgehead server,..which then sends it back to the 3rd Party Service. Around and around and around in circles is all it does. What are we doing wrong,...how should it be configured so that only Internet destined goes to the 3rd Party system while internal mails destined for internal users on the Second Exchange get properly routed there?
December 9th, 2010 9:45am

Where did you set the smart host? A lot of the instructions I see from third party providers have it set on the SMTP virtual server. That is wrong, and will cause issues that you are seeing. Despite attempts to get them to correct their documentation, I am usually ignored. When a smart host is set on the SMTP virtual server, all email goes through that smart host, no matter what else is configured. The smart host setting in that location is a hang over from the IIS SMTP that Exchange 2003 uses. You need to configure the smart host on an SMTP Connector. That will ensure that internal routing of email is not affected. http://www.amset.info/exchange/smtp-connector.asp Simon.Simon Butler, Exchange MVP Blog | Exchange Resources
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December 9th, 2010 11:40am

Thank you verey much Simon,...give me a bit to check this out! Phil
December 9th, 2010 11:47am

Oh, you asked about where it had been configured. Yes it was on the SMTP Virtual Server, and I had removed that because I was pretty sure it was causing the loop,...I just didn't know what to do with it after that. Anyway,...I just finished creating the Connector as you described. So lets see what it does,...fingers crossed. Phil
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December 9th, 2010 12:04pm

It has been in place a short time I and haven'y been able to confim it,..but I am fairly confident that this is the right solution so I will go ahead and mark is as the solution. I know what you mean about third parties not taking heed to being warned about things. I'm a Forefront MVP and have had similar cases with things related to ISA Server and third parties. Thanks Simon!
December 9th, 2010 3:11pm

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