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exchange 2003 hosting multiple domains

kjman asked
Medium Priority
Last Modified: 2010-03-05
My exchange 2003 server is working fine. I now have to host another domain on this server. The MX record for this second domain points to a different IP. i.e domainA.com = domainB.com = We own the IP's I have setup my firewall to for 1 to 1 NAT for the and configured my exchange server with another private ip address of I have also created a recipient policy with the new domain name and applied the policy to the users who need it, and i checked the box "this organization is responsible for" I then went to my default SMTP server, clicked the advanced tab, and added in the private ip so it would listen on it.

When i try and send an email to  user@domainB.com from an outside account I get a return message that says

Final-Recipient: RFC822; <user@domainB.com >
Action: failed
Status: 5.1.1
Diagnostic-Code: smtp; 550 5.7.1 Unable to relay for user@domainB.com

Am I on the right track here or way off?

Watch Question

Make sure that once you have created the policy, you right click on it and choose to apply this policy now, and hit yes, to apply now.

Might be one thing



Yea I did that, but still no luck. Am i on the right track here?
ikm7176Sr. IT Manager

you should point your MX record for DomainB to the same IP address as DomainA.

i.e DomainA-->  MX record= and
     DomainB---> MX record =

Since your exchange server is having 1 to 1 NAT with firewall. the mail for user@domainA.com is arriving to the IP address and then passed on to your exchange server (NAT rule). But the mail for user@domainB.com is arriving at IP address and ending up nowhere as your exchange is having 1 to 1 mapping with IP address
test your DNS report and MAIL test at  http://www.dnsreport.com
So change the MX record for domainB to IP address to allow the the e-mail flow.
change of MX record will take 48 hours to propogate to all the public DNS servers.

Hope this solves your problem .

Also check http://support.microsoft.com/default.aspx?scid=kb;EN-US;318635 for server configuration


But the mail for user@domainB.com is arriving at IP address and ending up nowhere as your exchange is having 1 to 1 mapping with IP address

Well I created a separate 1 to 1 NAT rule for to map to so this would mean that I have two 1 to 1 NAT rules configured. one for maping to and one for maping to With this in place I can send emails to user@domainA.com no sweat, and i know that the second 1 to 1 NAT rule on the firewall is setup correctly because when i send an email to user@domainB.com I get a unable to realy message bounced back to me. This tells me that the port 25 is open on the firewall for but its exchagne that doesnt like domainB.com

You are right though about making both domains MX records point to the same IP address, and i have done that. I think this will make things a bit less complicted, and easy to understand.

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