can not telnet port 25

[Feel Zhou]

Hello, My friend
This is Tom, I'm sending my greeting from China.
Today, one of my postfix server can not telnet any other mail server's port
25. It's working before 9:00am(bejing time CHina), I have restart the mail
server and reinstall the postfix. but it's looks like not working. How can
I fix this problem. Thanks for your help
TOM