nixCraft 🐧DNS settings to avoid email spoofing and phishing for unused domain https://www.cyberciti.biz/security/dns-settings-to-avoid-email-spoofing-and-phishing-for-unused-domain/
Aaron Longchamps@nixCraft shout out to Cloudflare who have this as a suggested action to take in their DNS dashboard if you're not using mail. It includes all the same settings, and is pretty much a one-click operation.