Moving from sendmail to postfix

[Graham S. Jarvis]

Hello,

I'm sure this is a really common question but google wasn't very helpful finding 
me the "one true answer" ;)

I run a MailScanner "hub" which processes mail for various domains.

Mail arrives at this hub because the MX10 record for those domains points to 
this host. Some addresses are local some have to be sent on to the final 
destination after having been scanned.

I had this set-up and working on a sendmail system using virtualusertable, 
aliases, access and mailertable and this works well.

I've now moved to Postfix and I need to know how to replicate the 
access/mailertable configuration so that I can list the domains where mail has 
to be forwarded and the IP_Addr of those hosts.

At the moment everything works fine for the local domains/addresses via
	virtual_alias_domains = /etc/mail/local-host-names
	virtual_alias_maps = hash:/etc/mail/virtusertable, hash:/etc/mail/aliases
in main.cf

BUT,
when a mail arrives for one of the domains that is not on this host I get a 
"(mail for domain.tld loops back to myself)" message and the mail is bounced.

I can understand that this is because the domain.tld has an MX10 that points 
back to me.

SO,
how to make sure that Postfix forwards directly to the IP_Addr like Sendmail 
used to..... ?

All help and pointers gratefully received!

Thanks in advance,

-Graham-