Hi Brian,

 

If you want each domain to have its own host name you need to do the following steps.  This does assume you have enough IP address for each domain that you want to have its own host name.

 

Login as the system admin and edit the domain.  Go to the Technical Tab and specify the Outbound IP address.  Then go to Settings | Protocol Settings | SMTP Out tab and change Outbound IP setting to "Use the domain IP".    After this go to Settings | Bindings | Hostname and add the outbound IP address with the appropriate host name.  This will only work if each domain has its own IP address.  If two of more domains share the same IP address it will default to the first one listed.