Setting up multiple mail domains while the exchange server is on a single active directory domain

440715 pts.
Active Directory
Microsoft Exchange 2003
Microsoft Windows Server 2003
Multiple email domains
Last year we had one active directory domain. For all intensive purposes, let’s call it With that domain, we had one IMail domain,, with proper DNS records and such. Six months ago, our company decided to branch off. So we created another IMail domain,, but we still only used one active directory domain. Currently, we have one active directory domain,, and two IMail domains, and All our users are setup as POP3/IMAP through various e-mail clients, IE Outlook, Entourage, webmail etc. We are currently setting up a Windows 2003 server for Exchange 2003 Enterprise. We set the server up as a domain controller for and went through all the other necessary steps. I’ve gotten so far as to setup two different mailbox stores and two different public folder stores for and Here is where my problem comes into play. I don’t know how to specify, through active directory, the mail domain for specific users. I can’t have all the users be set as when creating exchange mailboxes as their clients only know them through their address. I guess what I am asking is how do I setup multiple mail domains, for and, while the Exchange server is on the active directory domain?

Answer Wiki

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There are several ways to setup multiple domain on single Active Directory / Exchange domain. I am listing one which I used for my organization:

1. Create an OU for placing users of, say XYZ.

2. Create Universal Security Group for users with mail sending permission to all users, say XyzSec.

3. Create a Recipient Policy for, say with a custom filter rule using memberOf attribute (here filter rule will include memberOf XyzSec).

4. Create Address List for users so that users of other domain can easily find them in GAL.

5. If you want users to logon to their own domain, then you have to add UPN suffix to XYZ OU using ADSIEDIT tool.

6. In ADSIEDIT, locate XYZ OU under domainDNS class. Open Properties, under Attribute Editor tab you will find number of attributes.

7. Locate uPNSuffixes attribute and edit it to include

Now you are ready to create users for domain.

8. In Active Directory Users and Computers go to XYZ OU and create new users there.

9. Steps will be similar to normal account creation except you will find that here you can select either or domain because of the UPN suffix we added in steps 6 and 7. Here you have to select

10. After account creation done, add that user to XyzSec security group.

Now after a while this user will get smtp address once Recipient Policy created for this domain gets applied automatically. You can also apply this policy manually through Exchange System Manager.

Please remember, to append smtp address automatically to users following must be taken care:

1. Users must be created in XYZ OU and domain must be selected in Account Creation Wizard.
2. Users must be added to XyzSec security group so that they can pass memberOf filter rule created in Recipient Policy.

I hope this will address your query.

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  • Kurashige
    Hi, I have one question with the steps above. If for example we already have a default smtp email set into the recipient policy where we added before I even made this xyz OU. The users here are still using for logging in, and the email address using to send and receive is from And now, I wanted to do the to be added so that any new user that I could add can log in using and not the If I add this procedure, will it affect the receive and send of the users who are not inside the security group of xyz?
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