No one has idea ?
this is common practice for "unlimited domains" hosting
Client can alias as many webdomains as he wants. And to ensure no one is reseling his webhosting, emails can be set only on primary domain and rest are just domain aliases...
I'm really sad i cannot achieve this in ISPconfig with Domains module...
I think the design can be changed - if email domain will be set as alias, that system can set it also as email domain, if this is necessary