Rspamd Fast, free and open-source spam filtering system.
https://rspamd.com/comparison.html
https://rspamd.com/comparison.html
https://github.com/portainer/portainer
https://mailcow.github.io/mailcow-dockerized-docs/prerequesite-dns/
https://www.howtoforge.com/system-monitoring-with-sar-and-ksar
http://www.brendangregg.com/linuxperf.html
http://www.the-art-of-web.com/system/sftp-logging-chroot/