CentOS 6 comes with postfix and cannot send emails

After the postfix is installed through the rpm package that comes with CentOS 6, the mail-s... test fails. Maillog is as follows:
 
May 29 10:44:04 cl101 postfix/pickup [31536]: BA5662A0AFC: uid = 0 from = <root>
May 29 10:44:04 cl101 postfix/cleanup [31559]: BA5662A0AFC: message-id = <20130529024404.BA5662A0AFC@cl101.dev.bkjia.com>
May 29 10:44:04 cl101 postfix/qmgr [31537]: BA5662A0AFC: from = <root@cl101.dev.bkjia.com>, size = 3431896, nrcpt = 1 (queue active)
May 29 10:44:04 cl101 postfix/smtp [31561]: fatal: unknown service: smtp/tcp
May 29 10:44:05 cl101 postfix/qmgr [31537]: warning: private/smtp socket: malformed response
May 29 10:44:05 cl101 postfix/qmgr [31537]: warning: transport smtp failure -- see a previous warning/fatal/panic logfile record for the problem description
May 29 10:44:05 cl101 postfix/master [31534]: warning: process/usr/libexec/postfix/smtp pid 31561 exit status 1
May 29 10:44:05 cl101 postfix/master [31534]: warning:/usr/libexec/postfix/smtp: bad command startup -- throttling
May 29 10:44:05 cl101 postfix/error [31562]: BA5662A0AFC: to = <wmwu@bkjia.net>, relay = none, delay = 1.3, delays = 0.23/1/0/0.02, dsn = 4.3.0, status = deferred (unknown mail transport error)
 
This is because the postfix cannot read the service file. Check that the service permission is 640:
 
[Root @ cl101 etc] # ll | grep services
-Rw-r -----. 1 root 641243 Nov 7 2012 services
 
So change it to 644:
[Root @ cl101 etc] # ll | grep services
-Rw-r --. 1 root 641243 Nov 7 2012 services
 
Then try again to solve the problem.