Before anything we must describe you our network scenario. Our ISA server has the gateway specified for both, the internal and the external NIC configuration.
That is because with have VLans and the internal NIC need the gateway to properly communicate with the internal hots.
The IP for the MX record is different from the IP of the Checkpoint and we're routing the SMTP traffic between the Internet and the internal equipments. We have a Static NAT in Checkpoint capturing the traffic directed to the MX Record and redirecting it to the external ISA NIC IP.
Each time that we try a connection with a Telnet command to the port 25 we get the next error on the DOS Command : "Connecting To mail.domain.com ... Could not open connection to the host, on port 25: Connect failed"
And on the log of the ISA server we get a dinied error message. We think that It means that the comunication stop at the ISA External NIC.
I suspect that the problem could be the SMTP Inbound Rule, but I'm so confused.
hi I setup ISA 2004 behind Checkpoint firewall -1 NG a few months ago so our setups are nearly exactly the same.. If you have MSN send me a PM with your address and we can talk it over via MSN messenger its too difficult trying to troubleshoot this over a forum.