The Complete Guide to SPF, DKIM, and DMARC

Email authentication is the single most important thing you can do to stop attackers from impersonating your domain. This guide walks you through SPF, DKIM, and DMARC from first principles to production-ready DNS records -- with real examples you can copy and adapt. Why Email Authentication Matters Email was designed in an era when trust was assumed. The SMTP protocol has no built-in way to verify that the person sending a message actually controls the domain in the "From" address. That means anyone, anywhere in the world, can send an email that appears to come from your domain -- and most recipients will never know the difference. This is not a theoretical risk. Business email compromise (BEC) attacks cost organizations billions of dollars every year. A single spoofed email from your CEO's address can trick an employee into wiring funds to a fraudulent account. A phishing email that appears to come from your support team can harvest customer credentials. And even if your