What is DMARC Policy – None, Quarantine and Reject? How does DMARC Work

Email is the backbone of enterprise communication. But with over 330 billion emails sent daily, it’s also one of the most exploited entry points for cyberattacks. Threat actors have become increasingly sophisticated, relying on tactics like domain spoofing and email impersonation to infiltrate networks, deceive users, and commit fraud at scale. Their methods range from phishing scams disguised as trusted brands to advanced business email compromise (BEC) schemes targeting executives.

The misuse of email identities exposes enterprises to significant risks, damaging brand reputation, customer trust, and operational security. To address these threats, organizations must move beyond traditional spam filters and embrace email authentication frameworks such as Domain-based Message Authentication, Reporting & Conformance (DMARC) for a layered security protocol. Building on Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM), a robust DMARC policy not only enhances visibility into email traffic but empowers domain owners to instruct mail servers on how to handle unauthenticated messages.

If your role involves safeguarding email communication, here’s a detailed guide to understanding, implementing, and optimizing DMARC’s mechanics to protect your domain and organization.

What Is DMARC? 

DMARC, or Domain-based Message Authentication, Reporting & Conformance, is an email authentication protocol developed to combat email spoofing by validating the legitimacy of emails sent from your domain, giving domain owners the ability to protect their domains from unauthorized use. DMARC operates on three main policy levels: None, Quarantine, and Reject. Each represents a different stage of enforcement—from passive monitoring to active blocking. It builds on two existing standards—SPF (which verifies the sender’s IP address against authorized domain lists) and DKIM (which authenticates email integrity via cryptographic signatures).

Key Features of DMARC:

Identifier Alignment: Ensures the domain in the visible “From” header aligns with the domains authenticated by SPF and/or DKIM.

Control Over Email Handling: Allows domain owners to define how unauthenticated emails are handled by recipient mail servers.

Reporting Mechanism: Provides actionable feedback through aggregate and forensic reports to improve visibility and continuously refine email policies.

Why It’s Essential: Without DMARC, even organizations with SPF and DKIM in place remain vulnerable to spoofing schemes exploiting gaps in authentication headers. DMARC resolves this by enforcing domain alignment and providing clear instructions for unauthenticated emails.

The real innovation DMARC brings lies in its ability to enforce identifier alignment, ensuring the visible sender address (“From” header) aligns with the results of SPF and/or DKIM. Without DMARC, malicious actors can exploit loopholes in email headers to impersonate trusted brands—even if SPF or DKIM is technically present. Moreover, DMARC introduces a feedback mechanism. Organizations can receive two types of reports from receiving servers: aggregate reports, which provide an overview of authentication results across multiple messages, and forensic reports, which offer granular insights into individual authentication failures. This reporting not only helps detect abuse but also informs tuning decisions over time.

For any organization with a public-facing domain, a DMARC policy is not just a technical upgrade—it’s a necessary layer of defense in a world where brand identity is a frequent target of cyber threats.

How DMARC Works: The Technical Flow

The DMARC evaluation process follows a clear and structured workflow, initiated every time an email is received by a mail server. First, the recipient’s mail server checks the DNS records of the sending domain to determine if a DMARC policy exists. If found, the server proceeds to validate the message against both SPF and DKIM.

SPF validation ensures that the email originated from an IP address authorized by the domain’s DNS. DKIM, on the other hand, validates that the content hasn’t been tampered with by checking the digital signature embedded in the message. Crucially, DMARC requires domain alignment, where the domain in the visible “From” address must match the domain verified by SPF or DKIM. This alignment can be configured in strict (exact match) or relaxed (subdomain allowed) mode, via the aspf= and adkim= tags in the DMARC DNS record.

Once the checks are complete, DMARC instructs the receiving server on what to do with messages that fail authentication. This instruction is defined by the p= tag, which can be set to none, quarantine, or reject. Additional optional tags include:

rua=: Email address to receive aggregate reports.

ruf=: Email address to receive forensic reports.

pct=: Percentage of mail subject to policy enforcement.

fo=: Reporting options for failures.

This blend of policy and reporting turns DMARC from a static authentication tool into a dynamic system for ongoing visibility, control, and threat mitigation.

DMARC None: Establishing Visibility Without Disruption

A DMARC policy set to p=none serves as the observation deck in the journey to full enforcement. Under this policy, receiving servers evaluate SPF and DKIM alignment but take no direct action on messages that fail. Instead, they send back aggregate reports detailing who is sending mail on behalf of your domain and how those emails fare under authentication checks.

This non-intrusive approach is particularly valuable for enterprises with diverse email ecosystems. From marketing platforms and CRMs to billing and HR software, outbound emails often flow from numerous sources. Without first gaining visibility into this landscape, enforcing DMARC too early can disrupt legitimate business communication.

DMARC None is ideal for organizations that are just beginning to inventory their outbound email infrastructure. It helps identify misconfigured or unauthorized senders and pinpoints SPF or DKIM issues before recipients start rejecting messages. During this phase, reports should be monitored actively, which ingests XML data and transforms it into actionable dashboards for faster insights.

However, staying in “monitor-only” mode for too long carries risk. Without policy enforcement, attackers can continue spoofing your domain, eroding brand trust. To balance caution with security, organizations should treat DMARC None as a temporary intelligence-gathering phase, leading toward stricter policies.

DMARC Quarantine – Contain Suspicious Activity

A DMARC policy set to p=quarantine raises the enforcement level by instructing mail servers to route unauthenticated messages to recipients’ spam or junk folders. This intermediate step offers a compromise between outright blocking and passive monitoring, enabling protection while maintaining a safety net for potential false positives.

Quarantine is particularly valuable during progressive rollouts, which can be managed using the pct= tag. For instance, an organization may start by applying the quarantine policy to only 10% of messages, gradually increasing as confidence grows in the system’s accuracy. This staggered enforcement minimizes disruptions to legitimate mail streams—especially when coordinating across business units or third-party vendors.

That said, DMARC Quarantine introduces new operational considerations. Legitimate third-party senders must be correctly aligned with SPF and DKIM; otherwise, their messages risk being misclassified. Marketing and transactional platforms, in particular, often require DNS updates or DKIM delegation to function under quarantine. Enterprises should continue monitoring reports closely during this stage to catch anomalies and refine configurations. This phase also serves as an essential litmus test before advancing to full rejection. If the rate of false positives remains low and alignment scores are consistently high, the domain is likely ready for final enforcement.

DMARC Reject – The Gold Standard for Enforcement

The final and most stringent policy level is p=reject, where messages that fail DMARC authentication are outright rejected by the receiving mail server—never reaching the recipient in any form. For organizations with mature email infrastructures and stringent compliance mandates, DMARC Reject represents the gold standard of email security.

Reject policies offer powerful benefits. They significantly reduce the risk of phishing, especially spear-phishing campaigns that rely on spoofed executive identities. They also bolster brand integrity—customers and partners are far less likely to encounter fraudulent emails claiming to come from your domain. Over time, this contributes to improved deliverability and better sender reputation among major email providers.

Before implementing DMARC Reject, it is essential to complete a thorough technical readiness assessment. Every legitimate email source must have valid SPF and DKIM configurations. Internal teams and external vendors should be aligned, and any legacy systems should be audited for compliance. Industries with high regulatory exposure—such as financial services, healthcare, government, and SaaS providers—benefit most from Reject policies. These organizations handle sensitive information, face strict audit requirements, and are frequent phishing targets. In such environments, DMARC Reject is not optional—it’s expected.

DMARC Policy Management at Scale

For enterprise environments managing multiple domains, business units, or complex email infrastructures, scaling DMARC is not just about configuration, it is about synchronization The challenge isn’t setting a DMARC policy; it’s managing that policy across hundreds of moving parts, while maintaining enforcement without disruption.

This requires a unified, programmatic approach. DNS configurations must be meticulously aligned across SPF, DKIM, and DMARC records. Every third-party sender whether it’s a marketing automation platform, billing system, or CRM must be authenticated and monitored. Ownership must be clearly defined to avoid conflicts between IT, marketing, and external vendors. Centralized visibility becomes paramount. Without real-time dashboards and automated alerting, security teams are left blind to unauthorized senders or misaligned policy actions. That’s where dedicated tools make all the difference.

At scale, the true value of a DMARC policy isn’t just protection—it’s operational confidence. When domain governance is automated, visibility is continuous, and enforcement is resilient, security teams can move from reactive defense to proactive posture. That’s how modern organizations transform email from a risk surface into a trust signal.

Common Pitfalls and How to Avoid Them

While DMARC offers robust protection, its implementation is not without risk, especially in large or decentralized organizations. Understanding the most common pitfalls can significantly reduce misconfiguration and maximize the return on your email security investments. One of the most frequent issues is misaligned or improperly configured SPF and DKIM records. Even when a sender is authorized, if the domain identifiers do not align with the visible “From” address, DMARC will mark the message as non-compliant. This often happens with third-party senders like CRMs or newsletter services, which require explicit configuration to authenticate properly.

Another common oversight is failing to include all legitimate third-party email senders in your SPF record or DKIM setup. Many organizations rely on marketing tools, payment systems, or cloud-based communication platforms that send on their behalf. If these systems are not documented and integrated into the authentication process, critical emails may be misclassified or blocked.

A less visible but equally damaging mistake is ignoring DMARC reports. These reports contain detailed insights into how your domain is being used or misused and offer early indicators of problems in your email ecosystem. Without consistent monitoring and actionable review of these reports, you risk flying blind. 

Last but not the least, some organizations transition too quickly from DMARC None to DMARC Reject. Skipping the Quarantine phase or moving to full enforcement without proper validation can lead to the unintentional blocking of legitimate mail, resulting in operational and reputational issues.

The key to avoiding these pitfalls is a staged, data-driven approach. Map out every sender. Validate every configuration. Review every report. And treat DMARC not as a checkbox but as an ongoing discipline.

Conclusion

A strong DMARC policy goes beyond basic compliance—it provides operational control, protects your reputation, and reinforces trust with stakeholders. Each policy level plays a critical role:  DMARC None offers crucial visibility into email threats. DMARC Quarantine helps contain potential risks. DMARC Reject effectively blocks malicious actors from exploiting your domain.  

However, the real strength of DMARC lies in a well-planned, strategic implementation. It’s more than just meeting compliance standards—it’s about protecting one of your most valuable digital assets: your domain. In 2025, domain trust will equate to brand trust, making robust email authentication a business-critical priority.  For large-scale enterprises, the cost of ignoring DMARC is significant—impacting reputation, finances, and operations. Leading organizations recognize email authentication as foundational to cybersecurity, alongside identity management and zero trust principles.  Don’t stop at simply implementing DMARC. Actively manage, operationalize, and continuously improve it. Because the next cyberattack won’t hit your firewall—it’ll come from a fraudulent email that your DMARC policy could have prevented.

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