Yes, since I post the first message, I made exaustive tests.
I discovered I can't open TELNET sessions from any internal computer only to MX servers, on port 25.
I CAN (!!!!) open telnet sessions to SMTP servers, or to known testing routers (like R1R2 Cisco etc) and everything else. But when the connection is tryied to MX servers, it doesnt work
The server's motherboard is limited to one PCI interface, so I cant put it as the gateway for other computers.
But the strangest thing I saw is that from the WIN2K Pro gateway computer, I can't open the TELNET sessions to MX servers either.
I believe the DSL modem is blocking me to avoid MX packets to be exchageded.
It's a SPEED TOUCH PRO (Alcatel), and I searched a lot inside it for a filter or some "firewall" but I couldn't find it.
I ran out of solutions at this time, but I'll leave this post for others who face the same problem.
Regards,
Rafael Martin