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Email Spoofing (Email Spoofing)

Security Glossary - Email Authentication

Definition: Email spoofing is the practice of sending email with a forged sender address. Because the SMTP protocol does not inherently verify sender identity, anyone can send an email that appears to come from any address. SPF, DKIM, and DMARC were created specifically to detect and prevent email spoofing.

The Importance of Email Spoofing

Email spoofing is the foundation of most phishing attacks. An email that appears to come from your CEO, your bank, or your IT department is far more convincing than one from an unknown sender. Without email authentication (SPF, DKIM, DMARC), there is no technical mechanism to prevent anyone from sending email as your domain.

The damage from email spoofing extends beyond phishing. If attackers send spam using your domain, receiving servers may add your domain to blacklists, damaging your legitimate email deliverability. DMARC reporting helps you detect spoofing attempts and measure their volume.

Full protection against spoofing requires: SPF (to authorize sending servers), DKIM (to verify message integrity), and DMARC with p=reject (to instruct receivers to block unauthorized email). This combination does not make spoofing impossible, but it gives receiving servers the information to detect and reject spoofed messages.

How to Test for Email Spoofing

Use a DNS health checker to verify SPF, DKIM, and DMARC are all configured correctly. The goal is a DMARC policy of p=reject, which tells receiving servers to reject emails that fail authentication. Monitor DMARC aggregate reports to detect ongoing spoofing attempts.

Check DNS Health

Email Spoofing FAQ

Can someone still spoof my domain after I set up DMARC?
They can try, but receiving servers that check DMARC will reject or quarantine the spoofed messages. Not all receivers enforce DMARC strictly, but all major providers (Gmail, Outlook, Yahoo) do. DMARC with p=reject provides the strongest available protection.
How do I know if my domain is being spoofed?
DMARC aggregate reports (rua) show all servers sending email using your domain, including unauthorized ones. Set up DMARC with p=none and a reporting address to gain visibility into spoofing attempts before enforcing a reject policy.

Related Concepts

Phishing Sender Policy Framework DomainKeys Identified Mail Domain-based Message Authentication, Reporting and Conformance Email Deliverability
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