We often require notification and alerts from system to update/send. Recently I faced issue with a program sending email from linux(CentOS) which used postfix to relay emails, however it has security issues but as it was being used in a closed environment. After doing required standard configuration on postfix I faced following errors in maillog:
/etc/postfix/main.cf: Permission denied
I looked it up and got fixed after following command:
restorecon -r /etc/postfix