====== Postfix ======
  * [[https://habr.com/ru/companies/infowatch/articles/517896/|Особенности работы Postfix]]
  * [[https://linux-audit.com/postfix-hardening-guide-for-security-and-privacy/|Postfix Hardening Guide for Security and Privacy]]
  * [[https://www.linuxbabe.com/mail-server/setup-basic-postfix-mail-sever-ubuntu|Build Your Own Email Server on Ubuntu: Basic Postfix Setup]] - series of articles
  * [[https://www.postfix.org/BASIC_CONFIGURATION_README.html|Postfix Basic Configuration]]