Outgoing Mail Being Rejected

[shawnNC]

I have a Windows SBS 2003 setup with Exchange on a small network. It has a Private static IP address (192.168.1.X), and I have a router that is IP Masquarading with the Public Static Address. This Router is also port fowarding SMTP and POP to my Exchange server.

All users on the domain can send and revieve mail just fine, except sending to one domain which keeps rejecting us.

After sending mail to this domain there is a reply from System Administrator with Undelivarable Message as follows:

You do not have permission to send to this recipient. For assistance, contact your system administrator.
<mydomain.org#5.7.1 smtp;550 5.7.1 Email rejected due to sending server misconfiguration>

I went to dnsreports and everything passed, except the fact that I have 2 MX records pointing to the same IP Address. But I only have one IP address thats why. I felt like the domain who is rejecting me was doing some kind of reverse DNS lookup or something, and maybe this wasnt resolving right.

Does it have something to do with the fact that I am masquarading packets (NAT) and their server is rejecting this......(in other words, am I being seen as a spoofer, by their mail server)?

I have not had any problems with any other domain. I have contacted someone at the other organization, and they say that thier mail is working fine. The Exchange server is set up to run mail for the public doman. mydomain.org, but the server is also on a local domain address..... server.mydomain.local

Thanks in advance

Shawn


The users are in a partnership program with this domain, so its vital they can contact them

 

[shawnNC]

Never mind, the problem has been solved. I queried the other domains MX and found out they had an outside source for Mail. Did a who is on that domain, and found that it was owned by MessageDefense, a company who handles Spam Control. I contacted them, and had them whitelist me.

Everythings is working fine now