postfix SMTP problem

I've postfix + courier-imap + cyrus-sasl installed

Everything works well on local network (POP receive & send okay). Now I want it to allow me to send email on a remote network.

I use Eudora and everytime I tried to send an email on a remote network, it gives me a "connection refused" error.

Then I tried "telnet mail.server.ip.address 25" from a remote linux server and it got in, The weird thing is that when I telnet it in a dos shell on windows (also in a remote server), it dies out with connection failed error.

I guess this is not a problem with postfix, right? Maybe it's the router? or firewall? Any guide that I can follow to fix it? as the network wasn't set up by me so I've some difficulties to follow it up now.

I've been trying to figure it out for a week now but no luck... Any help or any idea would be really appreiated.

Thanks!!!

just a brief update, I've confirmed it's not my server problem at all. Some ISPs they just block the outgoing traffic of port 25