Struggling with Postfix configuration

[Alan Chandler <alan@chandlerfamily.org.uk>]

I have decided to switch from exim to postfix - but am struggling with a 
couple of parameters

I am sitting on a local lan behind a NAT gateway, so most of my machines have 
names of the form *.home  externally I appear to be the chandlerfamily.org.uk 
domain.

I have set the basic parameters as follows

mydomain=home
myhostname=mail.home
myorigin=chandlerfamily.org.uk
mydestination=chandlerfamily.org.uk, $mydomain localhost localhost.$mydomain


I was hoping that mail to xxx@kanger.home gets delivered locally, but it seems 
to being sent via the default transport (which is set to deliver to the smtp 
server of my ISP)

ACTUALLY I have an entry in /etc/aliases 


xxx : yyy@newdomain

SO actually what I really want is for the local deliver to look up xxx 
in /etc/aliases and forward (via smtp) to yyy@newdomain.

What do I have wrong in the basic parameters? 

-- 
Alan Chandler
alan@chandlerfamily.org.uk