Configuring postfix to handle email on multiple domains without being an open relay
Solution 1:
In your main.cf you need to set your mydestination parameter.
it should have something like:
mydestination = $myhostname, localhost.$mydomain, $mydomain
You need to change it to:
mydestination = $myhostname, localhost.$mydomain, domain.net, domain.com
More info on the parameter:
http://www.postfix.org/postconf.5.html#mydestination