Postfix and Selective Spam Filtering

Hi there

I use Postfix (1.1.11-20021115) on a FreeBSD 4.8 machine.
It handles mail for 4 of my domains all of which receive quite a bit of
SPAM.
I have added some effective SPAM filtering to main.cf and it rid me of 80%
of my SPAM.
I am also a backup for a friends email. He hosts a few sites for friends. He
uses MailScanner
on his server and it tags then delivers mail. The problem I have is my
mailserver is very strict
on what it lets through and it is deleting SPAM from my friends domains
without forwarding them
obviously. My questions is how can I turn SPAM filtering on for certain
domains only so that my
friends domains are not affected? I hope this makes sense. I will post the
relevant bits from main.cf
and transport files below.

Main.cf

virtual_maps = hash:/usr/local/etc/postfix/virtual
transport_maps = hash:/usr/local/etc/postfix/transport
empty_address_recipient = MAILER-DAEMON
mailbox_size_limit = 512000000000
message_size_limit = 102400000000
delay_warning_time = 4h
smtpd_helo_required = yes
disable_vrfy_command = yes

maps_rbl_domains =
relays.ordb.org,
opm.blitzed.org,
list.dsbl.org,
sbl.spamhaus.org,
blackholes.easynet.nl,
cbl.abuseat.org

smtpd_recipient_restrictions =
reject_invalid_hostname,
reject_non_fqdn_hostname,
reject_non_fqdn_sender,
reject_non_fqdn_recipient,
reject_unknown_sender_domain,
reject_unknown_recipient_domain,
reject_unauth_pipelining,
permit_mynetworks,
reject_unauth_destination,
check_recipient_access hash:/usr/local/etc/postfix/access,
check_sender_access hash:/usr/local/etc/postfix/access,
check_client_access hash:/usr/local/etc/postfix/access,
reject_maps_rbl,
permit

Transport File for backed up domains.
domain.com smtp:[ipaddress]
domain.co.uk smtp:[ipaddress]
domain.com smtp:[ipaddress]
domain.com smtp:[ipaddress]