When I try and send mail I see this in the maillog:
Sep 6 11:59:48 postfix/sendmail[11059]: fatal: open /etc/postfix/main.cf: Permission denied
But /etc/postfix/main.cf is world readable:
$ ls -l /etc/postfix/main.cf -rw-r--r--. 1 root root 27176 Jun 9 2014 /etc/postfix/main.cf