Question : Port 25 Open, all computers are ok, but one.

Hi!
I have a problem with Port 25 on one computer on the network. Case: corporate LAN, Windows 2000 Clients, and W2K Servers, Port 25 Open.
I have a small smtp utility for a specific task ('Advanced SMTP'), and it works on all computers, but on one it fails. Besides this, the computer is working great, it's the latest-fasted HP, configured the same way as the others.
Do you know what's causing this, and how to 'open' Port 25 (or fix it the problem other way)?
Thanks!

Answer : Port 25 Open, all computers are ok, but one.

not built in the os, but firewalls (XP has a built in one, but not 2000), a lot of AV products have one built in, as does (as mentioned above) the cisco vpn client
you can d/l msconfig for w2k here
http://www.perfectdrivers.com/howto/msconfig.html
then go tot he startup tab, and uncheck all but systray and explorer (if listed) and reboot and test, could be some third party app blocking it
also any errors in event viewer?