Internal DNS to external Mail Server

I host many different websites using IIS 6 on a server in the DMZ. To allow the users from my AD network access the websites on that server I have to enter a DNS setting directing www to the IP address of the DMZ server. Now, a new organization wants us to host their website on our server but they still will retain their emai server at their location. When I make the DNS changes to allow my users to access the website on the DMZ server any email being sent from our exchange server does not route to their server due to DNS issues. Can anyone tell me what I need to setup on my AD DNS to allow the mail to route to their server.
dkeddyAsked:
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ibiadmin6Connect With a Mentor Commented:
Is the web server sending the SMTP emails directly or relaying thru your internal exchange server?

if the web server is using the local smtp service setup the smart host on the SMTP service on the web server.
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cubeeqCommented:
Did you try to set up MX records for their domain in your DNS server?
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dkeddyAuthor Commented:
Yes, however I may have set it up incorrectly. If you have instructions please let me know.
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cubeeqCommented:
Ay, sorry. It is not there.

Create an SMTP connector in Exchange manager for that domain: Forward all mail to the smart host = their mail server and on the Address Space add SMTP + their-target-domain.

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dkeddyAuthor Commented:
Created the SMTP Connector however the mail will still not flow to that domain. I want to make certain that you know, this other mail server is not part of our network. The error I get from the Exchange System Manager is "Unable to bind to the destination server in DNS"
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MesthaCommented:
The SMTP connector method is the most efficient - as long as you are not using a host in the same domain name.

So if their domain is example.com, then the smart host you are entering should not be mail.example.com, unless you have an entry in your version of the DNS zone that points mail.example.com to their external IP address. If you are going to do that, then you may as well make the additional step of putting an MX record in the zone to point to mail.example.com as well!

You are basically doing a split DNS system.

-M
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