Setup External Mail server with Interworx

Our company have used interworx to handle about several domain client and many user email in each domain. We have bought new server for separate email server and main server, and we will separate mail server with the way according to Interworx FAQ :
http://interworx.com/support/docs/iworx-cp/sysadmin/system-services/mail-server/faq#external_mail_server
For setting dns server in main server is clear enaugh and added with explanation in: http://www.interworx.com/forums/showthread.php?t=632

The problem is how to install new server(with 1 new ip public) as mail server with supported application programs downloaded from interworx.
If we refer to how to install new server interworx in http://www.interworx.com/support/docs/iworx-cp/install/script-install , we must enter key license.Because we have owned 1 interworx unlimited domain license, then our company should not buy interworx license again because we only move mail server in main server to new server.

We still want to use easy way to set up and mange mail server in new server using interworx application.How procedure to install new server with only focussed as email server, so that nodeworx, siteworx, and webmail client in main server can handle it (Minimum can handle Mailbox in siteworx main server and siteworx client can manage member of his email domain)?

Please give me complete explanation about it!

the answer from support ticket

Thanks to Socheat Sou for the answer about this question[I have gave question with another sentences in support ticket but it’s like text in above --sorry for my bad english language–if it was happened :)]:

Posted On: 28 Sep 2007 10:17 AM
If the new server is also an InterWorx server, you will need to purchase a second license. InterWorx licenses are bound to one box, and one box only.
Socheat

Posted On: 02 Oct 2007 07:28 PM
Please note that InterWorx can’t control or manage mail for any external mail service. InterWorx can only manage and control mail services for the server it is on. The external mail service documentation is just telling how to disable the mail services on InterWorx for a domain, so they can be managed elsewhere, and InterWorx won’t try to take over mail for the domain.

However, one thing you can try is clustering the two boxes (server 1 and server 2), and then create a load balancing policy for just SMTP, POP3, and IMAP that does NOT include the cluster manager. This way, you’ll be sending all SMTP, POP3, and IMAP traffic to the 2nd server and still be able to manage it from the cluster manager (server 1).

Hope that helps,
Socheat