postfix能正常啓動，但無法發送郵件，
查看日誌文件（/var/log/maillog):
May 28 08:19:46 linux115 postfix/local[17523]: fatal: open lock file pid/unix.local: cannot open file: Permission denied
May 28 08:19:47 linux115 postfix/master[17517]: warning: process /usr/libexec/postfix/cleanup pid 17521 exit status 1
May 28 08:19:47 linux115 postfix/master[17517]: warning: /usr/libexec/postfix/cleanup: bad command startup -- throttling
May 28 08:19:47 linux115 postfix/master[17517]: warning: process /usr/libexec/postfix/local pid 17523 exit status 1
May 28 08:19:47 linux115 postfix/master[17517]: warning: /usr/libexec/postfix/local: bad command startup -- throttling
解決方法：
關閉selinux
[root@linux115 ~]#vi /etc/selinux/config
修改SELINUX爲：
SELINUX=disabled
重啓postfix服務，即可正常發出。