服务器无法发送邮件问题

CentOS 5.4 32位，安装了wdcp,环境是免费数据迁移时弄得。

网站程序是wordpress，回复邮箱提醒，或者是利用服务器发送邮件功能从来没成功过。
最近又安装discuz程序，还是不成功。测试phpinfo 显示[table=600,#ffffff,,0][tr][td]sendmail_path[/td][td]/usr/sbin/sendmail -t -i
[/td][/tr][/table]

php.ini里mail函数代码
[mail function]
; For Win32 only.
SMTP = localhost
smtp_port = 25


; For Win32 only.
;sendmail_from = me@example.com


; For Unix only.  You may supply arguments as well (default: "sendmail -t -i").
;sendmail_path =


; Force the addition of the specified parameters to be passed as extra parameters
; to the sendmail binary. These parameters will always replace the value of
; the 5th parameter to mail(), even in safe mode.
;mail.force_extra_parameters =