What is DMARC and how does it work effectively?

TL;DR:

Email remains the primary attack vector for cybercriminals, with phishing accounting for 16% of data breaches in 2025, making it one of the most common initial attack vectors [1]. Yet many organizations leave their domains vulnerable to spoofing and impersonation attacks simply because implementing email authentication feels too complex. DMARC (Domain-based Message Authentication, Reporting, and Conformance) provides a powerful solution to this problem, protecting your domain from unauthorized use while improving legitimate email deliverability. Read this blog to learn more.

• What is DMARC?
• How does DMARC work?
• DMARC records and domain alignment
• Benefits of DMARC implementation
• Implementing DMARC: Step-by-step guide
• Experience robust security with Red Sift OnDMARC

DMARC is an open email authentication protocol that enables organizations to protect their domains from unauthorized use, specifically from email spoofing, phishing, and Business Email Compromise (BEC) attack. It builds on two foundational email authentication standards: SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) [2].

At its core, DMARC allows domain owners to publish a policy in their DNS records that instructs receiving mail servers on how to handle emails that fail authentication checks. This policy can specify whether to accept, quarantine, or reject suspicious messages, giving organizations granular control over their email channel.

Beyond policy enforcement, DMARC provides a critical reporting mechanism. Domain owners receive detailed feedback about who is sending email on their behalf and whether those messages are passing or failing authentication. This visibility is essential for detecting and mitigating abuse, as well as for troubleshooting legitimate email delivery issues.

Understanding how DMARC functions requires examining the authentication standards it builds upon and the additional layer of protection it provides.

Before DMARC can work its magic, two foundational protocols must be in place. Think of SPF and DKIM as the security checkpoints that DMARC monitors and enforces.

SPF (Sender Policy Framework) specifies which mail servers are authorized to send email on behalf of a domain by listing their IP addresses in a DNS TXT record. When an email is received, the recipient's server checks if the sending server's IP matches one in the SPF record. It answers a simple but critical question: is this server allowed to send mail for this domain?

DKIM (DomainKeys Identified Mail) adds a digital signature to each outgoing email, which is verified by the recipient's server using a public key published in the domain's DNS. This ensures the email hasn't been altered in transit and confirms the sender's identity. It provides cryptographic proof that the message came from your organization and wasn't tampered with during delivery.

DMARC introduces a policy layer on top of SPF and DKIM through a clear step-by-step process:

1. Policy publication: The domain owner publishes a DMARC record in DNS. This record includes the policy (none, quarantine, reject), a reporting address for feedback, and other optional parameters.
2. Email receipt: When an email arrives, the recipient's mail server performs SPF and DKIM checks as usual.
3. Alignment check: DMARC requires that the domain in the email's "From" header (what the user sees) aligns with the domains validated by SPF (the "envelope from") and DKIM (the "d=" domain in the signature). This is called identifier alignment.
4. Policy enforcement: If both SPF and DKIM checks fail, or if they pass but don't align with the "From" domain, the recipient server consults the DMARC policy to decide whether to deliver, quarantine, or reject the message.
5. Reporting: The recipient server sends aggregate (RUA) and forensic (RUF) reports back to the domain owner, detailing authentication results and potential abuse.

A DMARC record is a DNS TXT record published at _dmarc.yourdomain.com that tells receiving email servers how to handle messages claiming to be from your domain. Understanding these records and domain alignment is essential for effective implementation.

A typical DMARC DNS TXT record looks like this:

v=DMARC1; p=reject; rua=mailto:dmarc-reports@example.com; ruf=mailto:dmarc-forensics@example.com; pct=100; adkim=s; aspf=s;

Domain alignment is the cornerstone of DMARC security. It ensures that the domain visible to the recipient in the "From" address matches the domain authenticated by SPF or DKIM. This prevents attackers from using your domain in the visible "From" field while sending from their own authenticated infrastructure.

Alignment can be strict (exact match required) or relaxed (subdomain match allowed). Most organizations start with relaxed alignment during implementation and move to strict alignment for maximum protection.

DMARC implementation delivers measurable advantages that directly impact organizational security, operations, and bottom-line performance.

Organizations with DMARC enforcement at "reject" block nearly all direct domain spoofing attempts when receiving mail servers properly enforce the policy, eliminating a major attack vector used in BEC campaigns that cost businesses over $2.9 billion in 2023 [3]. The average BEC attack costs $135,000, but the reputational damage extends far beyond immediate financial losses when customers receive fraudulent emails from your domain.

Email providers evaluate sender reputation when deciding inbox placement. Domains with DMARC enforcement signal to providers like Gmail, Outlook, and Yahoo that the organization takes email security seriously, resulting in preferential treatment during delivery decisions.

Organizations implementing DMARC typically see up to 10% improvement in email deliverability rates, fewer legitimate emails flagged as spam, and higher engagement on marketing campaigns. Sales teams get faster response times, and customer communications land reliably in inboxes.

DMARC reports provide comprehensive visibility into your email ecosystem, revealing third-party vendors, legacy systems, marketing platforms, and departmental tools you didn't know were sending email. This visibility enables security teams to identify unauthorized sending attempts, discover shadow IT before incidents occur, and meet regulatory requirements from frameworks like HIPAA and PCI DSS. Organizations gain definitive answers about who sends email on their behalf, backed by daily reporting data.

Manual DMARC implementation requires parsing thousands of XML reports, identifying legitimate versus malicious senders, and coordinating with multiple third-party services. Red Sift OnDMARC simplifies this complexity, enabling organizations to achieve full enforcement in 6-8 weeks, though timelines vary based on infrastructure complexity.

• Automated report analysis: Visual dashboards transform complex XML into actionable insights showing authentication trends and failing sources
• Guided policy progression: Clear recommendations on when to safely move between policy levels with confidence scores
• Complete email source discovery: Automatically identify all services sending email on your behalf with authentication status
• Simplified configuration: Step-by-step instructions tailored to each platform with verification steps
• Continuous monitoring: Alerts for new email sources, authentication failures, and spoofing attempts

OnDMARC makes enterprise-grade email security accessible without requiring deep technical expertise or months of implementation time.

With BEC attacks costing organizations billions annually and email deliverability increasingly dependent on proper authentication, DMARC implementation should be a top priority for IT and security teams.

Red Sift OnDMARC makes implementation fast and effective. Start your 14-day trial and join 1,200+ organizations protecting their domains with enterprise-grade email security.

Get a free cyber risk assessment by booking a short demo and take the first step toward comprehensive domain protection.

[1] Verizon 2025 Data Breach Investigations Report: https://www.verizon.com/business/resources/Tea/reports/2025-dbir-data-breach-investigations-report.pdf [2] NIST Special Publication 800-177 Revision 1 - Trustworthy Email: https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-177r1.pdf [3] FBI IC3 Report - Business Email Compromise Statistics: https://www.ic3.gov/Media/PDF/AnnualReport/2023_IC3Report.pdf