How to allow mail relay of specific IP address
I have set up an anti-spam relay server (RH Linux 8 postfix, amavis, spamAssassin) between my mail server and the Internet. As such, I have enabled relaying from my mail server only in order to avoid becoming an open relay. However, I have an off-site server farm that sends email messages to acknowledge receipt of submissions. These of course fail because I don't allow relaying. So my clients don't get their confirmations. My question is, can I configure a specific public IP address to allow relaying from or will this create an open relay? My CIO says that it will not but I'm not convinced and my tail is on the line if I open one up. I can't use pop before smtp because this process doesn't check for mail.
Can anybody point me in the right direction?