Mail server Cennection timed out for all smtp server

[totiz]

I'am newbie for mail server.
After I install CentOS 5.2.
I try to send mail to my email.
but It' not work. I get error msg from /var/log/maillog follow below.

Jul 9 06:26:47 XXXXX sendmail[6025]: m687K2op001151: to=<XXXX@gmail.com>, delay=16:06:45, xdelay=00:14:03, mailer=esmtp, pri=1561040, relay=gsmtp183.google.com. [64.233.183.27], dsn=4.0.0, stat=Deferred: Connection timed out with gsmtp183.google.com.

I think problem come from firewall in CentOS(Both Firewall and selinux are disable).
Because I try "telnet gsmtp183.google.com 25" I can't connect.
while I try in Windows XP that respond "220 mx.google.com ESMTP f4si49893210nfh.27".

(Both Windows XP and CentOS are same network)

Please advice me for solve this problem.
Thank you.

[Lazydog]

I think problem come from firewall in CentOS(Both Firewall and selinux are disable).

How or why do you think it is the firewall?