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sifugregFlag for United States of America

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DNS can't get mail to outside domain when partially hosted inside

Let's see if I can explain this.  I host the portal server of a clients domain on my server farm.  Externally everything works fine.  DNS records were updated appropriately.  Obviously, because these machines are NAT'd, th internal address is different from the external causing me to maintain my own DNS zone for the domain.  Again, all works well with the exception of sending the client emails.  In my DNS zone, I've created the following:

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"Portal" is the machine on my network where all other aspects of their domain exist outside (hosted on network solutions servers) with public addresses partially obscured to protect the innocent.

I can Ping both and and get the same address back but if I send an email message to "" my exchange server brings me back a mail delivery error of "503 you must authenticate first".  If, however, I send an email to it appears to go through.  I have another client that shows identical DNS entries and it works fine.  What am I missing?
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Simon Butler (Sembee)
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You need a host name that points to their mail server and then create an MX record that uses that host name.  
Therefore as long as their domain isn't on your Exchange server in any shape or form, the email will be delivered.

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I did that previously and got the same results.  I put it back in ( A record for and a MX record pointing to that FQDN) and nothing changes.
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Self diagnosed and fixed.