The instructions for doing this type of thing are documented here. http://www.postfix.org/RESTRICTION_CLASS_README.html
try something like this in
/etc/postfix/main.cf :
smtpd_recipient_restrictions =
check_client_access hash:/etc/postfix/inside_ips
...the usual stuff...
smtpd_restriction_classes = insiders_only
insiders_only = check_sender_access hash:/etc/postfix/insiders, reject
/etc/postfix/inside_ips :
192.168.1 insiders_only
192.168.2 insiders_only
/etc/postfix/insiders :
my.domain OK matches my.domain and subdomains
another.domain OK matches another.domain and subdomains