I am planning to upgrade several 5.1.2 servers to 5.6 in a week or so.  One issue I need to resolve is allowed relaying which I have set up for 2 users on a 5.1.2 server.  I have allowed 2 single IP address (mask 255.255.255.255) to relay from the internet in my smtpd_check_rules config.  Can I configure 5.6 to allow internet relay for 2 individual IP addresses?  I am trying to avoid reliance on PPTP or IPSEC vpn for this situation.
Any help is appreciated. 
ryan