Written by: Kelsey Clark, Fortress SRM Security Innovation & Brand Strategy Leader
The Hidden Risk Inside Your Inbox
Email is the communication backbone of modern work, but it’s also a top target for attackers.
Phishing, spoofing, and impersonation attacks exploit the fact that email was not designed with strong identity verification. As these attacks grow in sophistication, security teams face increasing pressure to protect both their organization and their people.
This is where DMARC (Domain-based Message Authentication, Reporting, and Conformance) can help.
What DMARC Does
DMARC helps receiving mail servers determine whether messages claiming to come from your domain are legitimate.
When implemented correctly, it reduces the risk of attackers impersonating your organization, protecting your employees, customers, and brand reputation.
While primarily a security tool, DMARC also supports trust and compliance by:
- Demonstrating that your emails are legitimate.
- Providing visibility into who is sending email on behalf of your domain.
- Helping you meet email authentication requirements that may support regulatory compliance.
How DMARC Works
DMARC builds on two key email authentication technologies:
- SPF (Sender Policy Framework): Verifies the sending server is authorized.
- DKIM (DomainKeys Identified Mail): Uses cryptographic signatures to ensure integrity.
On their own, SPF and DKIM are useful but incomplete. SPF can fail in forwarding scenarios, and not all senders consistently sign with DKIM. DMARC strengthens protection by requiring that at least one of these technologies passes and that the domain used aligns with the visible “From” header. This alignment check makes impersonation much harder.
- SPF Alignment: Confirms the sending server is authorized and its domain matches the “From” domain.
- DKIM Alignment: Confirms the message signature is valid and the signing domain matches the “From” domain.
If either SPF or DKIM aligns, DMARC passes. If neither aligns, DMARC applies the policy you’ve set—monitor, quarantine, or reject.
The diagram below illustrates this difference: before DKIM, DMARC relies solely on SPF alignment. After DKIM, DMARC can validate alignment with either SPF or DKIM, providing stronger, more reliable protection against spoofing.
Throughout this process, DMARC also generates reports that give you visibility into who is sending emails on behalf of your domain and which messages fail authentication. This combination of verification, alignment, policy enforcement, and reporting reduces spoofing, improves trust in your emails, and gives you actionable insight into your email ecosystem.
⚠️ Limitations: DMARC stops exact-domain spoofing, but not lookalike domains or compromised accounts.
It’s important to note that DMARC primarily protects against exact-domain spoofing. Lookalike domains, display name impersonation, and compromised accounts can still bypass these checks. For complete protection, DMARC should be implemented as part of a broader, layered email security strategy.
Why DMARC Matters for Your Organization
Email-based impersonation isn’t just an IT issue, but it’s a major business risk.
Without DMARC, there’s a better chance attackers can:
- Send fake invoices or phishing emails that put customers at risk
- Trick employees into sharing credentials or sensitive data
- Damage your organization’s reputation
With DMARC, you gain:
- Trustworthiness: Your emails are verifiable
- Visibility: Reports show domain usage
- Control: You decide how unauthorized emails are handled
- Confidence: Supports compliance and customer trust
Best Practices for Implementing DMARC
Rolling out DMARC isn’t a one-click solution. A strategic, phased approach will help you protect your domain without disrupting legitimate email flow.
- Start with Monitoring: Use a “none” policy to gather data without impacting delivery.
- Align SPF and DKIM: Ensure both are correctly configured and aligned with your “From” domain (strict vs. relaxed alignment per RFC 7489).
- Sign Outgoing Mail: Use DKIM on all messages to verify authenticity.
- Review Reports: DMARC aggregate (RUA) and forensic (RUF) reports are in XML format and difficult to read. You’ll need proper tooling to parse and act on them. Analyze who is sending emails on your behalf.
- Gradually Enforce: Move from “none” to “quarantine” or “reject” to actively block spoofed messages, but be cautious. Jumping too quickly to “reject” can break legitimate third-party senders (CRMs, payroll services, marketing automation).
- Include Subdomains: Protect all parts of your domain.
- Educate Your Team: Train employees on phishing risks and DMARC’s role in your policy.
- Maintain and Evolve Your Setup: Email infrastructure changes over time. Keep DMARC records up to date, and review policies regularly.
Beyond DMARC: Layered Security
DMARC is powerful, but most effective when combined with broader security measures:
- Ongoing user awareness training, including interactive tabletop exercises.
- Regular patching and proactive cybersecurity measures to maintain strong cyber hygiene.
- Incident response planning to prepare your team for attacks before they happen.
Fortress SRM Can Help
Email spoofing and phishing aren’t going away, but DMARC gives your organization a strong defense. Implementing it can be complex, but you don’t have to go it alone.
The Fortress Security Risk Management team provides hands-on support for DMARC and broader email security as part of a holistic cybersecurity strategy. We work alongside you to identify risks, strengthen defenses, and simplify complexity. With our co-managed services, you get the right mix of guidance and support to match your security maturity, making security clear and manageable.
Take Action Today
Request your Fortress SRM DMARC assessment and start protecting your domain, your customers, and your business.
Fill out the form below or connect with Kelsey on LinkedIn to start the conversation.