Have you faced the problem of hosting xyz.com on a server and another domain abc.com on the same domino server and providing email addresses on the different domains? Well, one way if ound out to do that was to host the server using the main domain (xyz.com) For the additional adbc.com the DNS settings should point to the IP of xyz.com. Specify the Internet address of the user as email@example.com. If this option is not available or you would like to provide different aliases, edit the person document User field and add the values as desired.
For ex: the user will be registered as firstname.lastname@example.org To ensure that mails are delivered specify the Internet address as email@example.com. To provide an alias such as firstname.lastname@example.org put that entry in the user field of the person document. With a bit of scripting you can let the user do it from his browser as well. I hope that this would be useful.