====== External documentation ======
  * [[https://frightanic.com/apple-mac/thunderbird-icloud-calendar-sync/ | iCloud calendar in Thunderbird]]
  * [[https://forum.dd-wrt.com/wiki/index.php/Tutorials | DDWRT Docs]]
  * [[https://serverfault.com/questions/163111/allow-traffic-to-from-specific-ip-with-iptables | Whitelisting IPs with iptables]]
  * [[https://wiki.archlinux.org/title/Router#With_systemd-networkd | Archlinux as router]]
  * [[https://nmap.org/book/man-port-scanning-techniques.html | nmap techniques]]
  * [[https://www.twilio.com/docs/sendgrid/for-developers/sending-email/integrating-with-the-smtp-api | Sendgrid email API]]
  * [[https://confluence.atlassian.com/adminjiraserver087/migrating-jira-applications-to-another-server-998871666.html | Jira Migration]]
  * [[https://docs.gitea.com/administration/backup-and-restore | GITEA backup and restore]]