Question : relaying denied IP name lookup failed

I've been through every question on the board about the 5.7.1 NDR but the solutions are not working.

Here's the skinny:

I am in the military and my unit sets up deployable servers during contingency operations.  We have a new set of equipment running windows 2003 enterprise server and Exchange 2003 standard server.  We have sidewinder 5.2.1 firewall and a router configured for 3 subnets 192.168.14.0, 192.168.11.0 and 192.168.20.0.  The 20 subnet has an external DNS server (not a fake root host) which has info for each of the external burbs of the firewalls  (14.0 and 11.0) and MX records for both.

When we try to send mail from the outlook client on one domain to a client on the other domain we recieve a NDR.  specifically
SMTP 550 5.7.1.
You do not have permission to send to this recipient
relaying denied IP name lookup failed (IP of the mailserver)

When I do an nslookup and put in IP addresses, they resolve for all of the machines on my networks.  So I don't understand at what point the IP name lookup failed.

I've also ensured that the relay access list is on authentication and that every computer on the mail server's class B is on there (192.168.0.0) and it still denies.

since this is training for what we do out in the field, we were following the manuals sent from the government contracted corporation, however, I really want to get this to work.

I've gone through all the common aspects of the exchange portion and I was thinking it might have something to do with the firewall, but I have no way of tracking down where the mail goes.

Any help would be appreciated.

Chris

Answer : relaying denied IP name lookup failed

>When I do an nslookup and put in IP addresses, they resolve for all of the machines on my networks.  So I don't understand at what point the IP name lookup failed.

By default Sidewinder uses its own internal DNS server, so the SMTP relay inside Sidewinder will lookup DNS PTR records from this rather than from the DNS server that your workstation queries.

http://www.securecomputing.com/pdf/g2_611_an_multiburbsendmail.pdf might help, ignore the high availability stuff in it.