Restricting Intra-Office Receiving

[Asai]

Greetings,

I've worked out how to restrict intra-office sending from a user to a 
user, but I'm a bit stumped on how to restrict intra-office receiving; 
restricting from who a user can receive mail.

This is what I have at this point:

smtpd_recipient_restrictions =  permit_sasl_authenticated,
        reject_invalid_hostname,
        reject_unknown_reverse_client_hostname,
        reject_non_fqdn_sender,
        reject_non_fqdn_recipient,
        reject_unknown_sender_domain,
        reject_unauth_destination,
        check_recipient_access 
mysql:/etc/postfix/mysql_restricted_recipients.cf

Can someone point me in the right direction?

Thanks.

--
--Asai