virtual and local delivery

Hi,


I'm trying to learn how to differentiate between local and virtual delivery
on postfix, but i'm a bit stuck.

Can someone tell me what keywords specify the behaviour in postfix for
allowing/disallowing local delivery (i assume local delivery means via
checking the /etc/passwd file) ?

I'm also trying to figure out how i can have the system behave like this:


first check if the user exists on the /etc/passwd file, if it does, try to
deliver locally to /var/spool/mail/username
if the user is not defined in /etc/passwd, go check with an ldap directory.


the ldap part i've already got working, but it seems to have disabled local
delivery ? can't i have both of them at the same time ?


Or if anyone knows some documentation that specifically adresses this issue
(i coudn't find anything appropriate on the postifx.org site).



thanks,


Tom.