I'm not able to access my smtp server outside of the network. Initially my thought was firewall... But I double and triple checked; as well as had two others verify that port 25 IS being forwarded to the Exchange box. I'm able to telnet into it inside the network, or using VPN without any problem.
It's running Exchange 2003 SP2 on Windows Server 2003 firewalled by a SonicWALL TZ-170 with content filtering and IPS. No logs can be found on the firewall in reference to port 25.