554 rDNS error – Postfix Question

Hello,

Last December I purchased an XServe for our office to host Leopard File, internal DNS, and Open Directory (master) services. A few weeks later I setup a clean Leopard Mail Server. Our external DNS is still hosted by our ISP. The Mail serve also acts as an OD replica. To date everything has run swimmingly, no issues, and reverse DNS lookups for our internal network have worked fine.

Yesterday I found out that mail sent from our server is being returned with 554 errors. So I sent some email from the server to my home email acct and started investigating the header info. Here is the line that piqued my interest:

“Received: from mail.finishedart.com (unknown http://216.24.175.242) by mail.comp-b.com (Postfix) with ESMTP…”

The external IP for mail.finishedart.com is NOT 216.24.175.242, it is 216.24.175.201. A “dig -x 216.24.175.201” returns the correct PTR record. “dig -x 216.24.175.242” returns no PTR. In fact the x.x.x.242 ip isn’t even in my alloted block of IPs from my ISP.

Can anyone shed any light on when the line above is generated? Is it from Postfix when the mail is sent? Or does the receiving server do a lookup of my domain and create this line in the header?

I’ve given both the mail and dns servers a good going over and haven’t been able to shed any light on this. Postfix seems to be correctly configured, with the exception being that every email sent turns out to have this erroneous IP address in the header. Likewise the DNS server doesn’t even contain records for the finishedart.com domain, only finishedart.lan (our internal network). The external .com domain is handled by our ISP. They are telling me that everything is configured correctly on their side.

Thanks in advance for any help you can offer.