If you have qmail installed on your server and if it is already accepting mails for some specific domain, you may want to add a new domain for which you may like your server to accept mails for more domains. This is usually required either so that your server will relay those domains or it will accept mails even for these domains. This task is very simple to accomplish. If you want your server to relay mails coming to any domains, you need to add that domain in rcpthosts file in /var/qmail/control. If you want your server to accept mails to another domain also, then you will have to add that domain in locals file in /var/qmail/control.