I have an Exchange 2003 SP2 server on Server 2003 that is a DC and DNS server. I have 3 domains and a few users use POP3 to get mail from outside my network which works fine. When they try to send mail from outside my network they can't authenticate.
This worked until I added a Server 2008 R2 DC to the network yesterday. The server 2k8 machine only has AD and DNS installed on it.
No issues with AD synchronization between them.
All other mail seems to be working fine.
Is there something in the authentication with Server 2k8 R2 that could be causing this to fail?