Postfix Docs

http://www.postfix.org/documentation.html

https://easyengine.io/tutorials/mail/postfix-queue/

https://wiki.centos.org/HowTos/postfix_restrictions

Postfix 실행제한

https://www.reddit.com/r/postfix/comments/6fk9mj/restrict_access_to_the_mail_queue_use_of_the/