5.5.0 NDR when sending to certain domains

[AirGibson]

I've searched high and low for a solution to this. When I send e-mail from my Exchange 2000 server to certain domains (such as AOL.COM), I receive this NDR:

There was a SMTP communication problem with the recipient's email
server. Please contact your system administrator.
<osa.comax.com #5.5.0 smtp;550 REQUESTED ACTION NOT TAKEN: DNS FAILURE>

After looking around, it seems this is commonly caused by a failed reverse DNS lookup. I assume this means that the aol.com servers tried a reverse dns lookup on my server's IP, and did not receive anything. To check this, I've used nslookup to check my IPs, and they seem to be resolving just fine. Perhaps I'm checking them improperly.


I suspect it is due to this:

My internal network has a domain name of &quot;osa.local&quot; along with it's own internal DNS. My mail server is &quot;ash.osa.local&quot; and has an internal IP of 192.168.0.227. The router does NAT for that address to change it to the external address of 64.18.101.227 which is &quot;osa.comax.com&quot;.

I'm betting that somehow the servers such as AOL.COM are trying to do reverse lookup on &quot;ash.osa.local&quot; and, obviously, it's going to fail if it does that. I'd have no idea how to fix this other than totally changing the network's domin name from &quot;osa.local&quot; to &quot;comax.com&quot;. Any suggestions?

 

[AirGibson]

Nevermind. I found the answer. The problem was that my Exchange 2000 server users had their &quot;@osa.local&quot; addresses listed as their primary address. I switched their primary addresses to their &quot;@osa.comax.com&quot; addresses and everything works fine now.