Problem with Postfix Mail Server
 

Dear friends,
As you know by using "virtual" facilities in postfix we may serve more than one domains at a time.
I wish to know I can create :
sales@demo.com
sales@omed.net
while all of the mentioned solutions in postfix docs will reach to the Unix usernames?(two username and same name!).
So , how I can create these users in my mail server machin?
Postfix 2.2.5
Linux FC4


Thank you ,