Summary
Implementing a DMARC policy with p=reject offers the strongest protection against email spoofing and phishing, but it also carries the highest risk of blocking legitimate emails if not managed carefully. The primary concern often revolves around how such a strict policy impacts legitimate emails that might be auto-forwarded, as forwarding can sometimes break DKIM authentication, leading to DMARC failures. A phased implementation approach, starting with monitoring and gradually increasing enforcement, is widely recommended to mitigate these risks. This allows senders to identify and resolve issues with legitimate email streams before they are rejected.
Key findings
- Gradual rollout: Moving from p=none to p=quarantine and then p=reject in stages (e.g., 25%, 50%, 75%, 100% enforcement) is the safest method to assess impact.
- Monitoring is crucial: Consistently reading DMARC aggregate reports (RUA) is essential to identify legitimate email sources that are not yet DMARC compliant.
- Auto-forwarding concerns: Auto-forwarding can break DKIM authentication, leading to DMARC failures for legitimate emails. However, major mailbox providers often maintain lists of forwarding domains to mitigate this.
- Security vs. deliverability: While p=reject offers maximum brand protection, some organizations opt for p=quarantine at 100% to reduce deliverability risks while still gaining significant security benefits.
Key considerations
- Comprehensive email audit: Before moving to p=reject, ensure all email sending sources are identified and properly configured with SPF and DKIM. This prevents legitimate emails from being blocked.
- Subdomain strategy: For complex organizations, using subdomains for specific email streams can provide more control and make DMARC implementation easier.
- Cross-departmental visibility: Lack of awareness about all email senders across different departments can lead to unexpected email rejections when moving to p=reject. A centralized inventory is vital.
- Compliance implications: DMARC reports are essential for ensuring compliance across all email sending activities, providing visibility into potential issues that might otherwise go unnoticed due to organizational silos.
What email marketers say
Email marketers often approach implementing a p=reject DMARC policy with a blend of enthusiasm for enhanced security and apprehension regarding potential deliverability impacts. The fear of legitimate emails failing to reach recipients, particularly those relying on auto-forwarding, is a recurring theme. Marketers emphasize the importance of methodical testing and careful observation of email flow to ensure that security measures don't inadvertently disrupt critical communications, such as transactional emails.
Key opinions
- Phased approach preferred: Many marketers agree that a step-by-step rollout from p=none to p=quarantine and then p=reject, often using percentage values, is the safest way.
- Transactional email vulnerability: There's a significant concern that critical transactional messages, especially when auto-forwarded, could be negatively impacted or blocked by a strict DMARC p=reject policy, leading to lost communications with users.
- ISP sophistication: Some marketers have observed that major email providers (like Gmail, Hotmail, Yahoo) are becoming more adept at handling forwarded emails, maintaining lists of forwarding domains to ensure legitimate mail is delivered.
- Pre-DMARC authentication: Marketers stress the foundational role of configuring SPF and DKIM before DMARC is set to enforce policies, preventing initial delivery issues.
- DMARC reports: Regular review of DMARC reports is considered essential to identify any legitimate emails that are not authenticating correctly, allowing for adjustments before moving to a stricter policy. Monitoring DMARC can help.
Key considerations
- Thorough testing: Implement a rigorous testing phase using a percentage-based rollout to observe and address any unforeseen deliverability issues, especially for complex email setups. Safely transitioning your DMARC policy is key.
- Authentication alignment: Ensure that all legitimate email sending services are properly aligned with your domain's SPF and DKIM records to prevent false positives and maintain a high deliverability rate (as mentioned in a guide to advancing DMARC policies).
- Risk assessment: Consider if the enhanced security of p=reject outweighs the minimal risk of using p=quarantine at 100%, especially for organizations with a high volume of crucial transactional emails.
- Subdomain confidence: If a subdomain is used solely for email sending, marketers often feel more confident in moving to a stricter DMARC policy due to greater control over its email sources.
Marketer view
A marketer from Email Geeks expressed concerns about setting a DMARC p=reject policy due to potential harm to legitimate email deliveries, especially for users with auto-forwarding rules that might create DKIM violations.
Marketer view
An Email Geeks marketer noted that starting with a small percentage and gradually increasing the DMARC policy enforcement is an excellent testing strategy to observe impacts and minimize risks.
What the experts say
Email deliverability experts universally advocate for a cautious, data-driven approach when moving to a DMARC p=reject policy. They highlight the critical importance of DMARC reports (RUA) in uncovering all legitimate sending sources and monitoring for any authentication failures, including those caused by mail forwarding. Experts often share real-world examples of severe outages caused by hasty DMARC implementation, underscoring the necessity of a methodical transition to avoid accidental blocking of essential communications. They stress that comprehensive visibility across all email streams is paramount, especially for complex organizations with multiple departments sending mail.
Key opinions
- Phased implementation is best: Experts strongly recommend a gradual transition from p=none to p=quarantine and then p=reject, using percentage-based enforcement to test impacts. See simple DMARC examples.
- DMARC reports are essential: Actively reading and analyzing DMARC reports is critical for identifying and resolving issues with legitimate unauthenticated mail before increasing policy enforcement.
- Visibility challenges: Experts highlight that a significant challenge in implementing p=reject is the lack of a centralized inventory of all email sources across an organization, which can lead to unexpected rejections.
- Real-world risks: Cases like GitLab's outage, where DMARC misconfiguration led to critical email failures, serve as stark warnings about the potential impact of improper p=reject implementation.
- Compliance is broader than subdomains: While subdomains offer more control, compliance and DMARC enforcement should encompass all email streams from a domain, not just dedicated subdomains.
Key considerations
- Comprehensive audit: Conduct a thorough audit of all existing email sending services and ensure they are properly authenticated with SPF and DKIM before moving beyond p=none.
- Continuous monitoring: Maintain ongoing vigilance by reviewing DMARC reports regularly, even after reaching p=reject, to catch any new or changed sending sources. The Threatcop blog reiterates this.
- Internal communication: Establish clear communication channels across departments to ensure all email sending activities are known and accounted for, preventing accidental blocking of crucial internal or external communications.
- Understand forwarding: While mail forwarding can cause DKIM failures, understand that major mailbox providers are often equipped to handle these scenarios without rejecting legitimate mail, especially for well-known forwarding paths.
Expert view
An expert from Email Geeks recommends starting with a DMARC p=none policy and diligently reviewing legitimate unauthenticated mail in RUA reports before progressing to stricter policies.
Expert view
An Email Geeks expert advised that the safest way to implement DMARC p=reject is to first transition to p=quarantine and gradually increase the enforcement percentage, for instance, from 25% to 100%.
What the documentation says
Official documentation and authoritative guides on DMARC emphasize its role in combating email fraud and spoofing by providing senders with control over unauthenticated messages. They consistently highlight the importance of the preparatory steps: establishing proper SPF and DKIM authentication, starting with a monitoring-only policy (p=none), and meticulously analyzing DMARC reports. The transition to a p=reject policy is presented as the ultimate goal for maximum protection, but only after ensuring all legitimate email streams are fully authenticated and visible through reporting.
Key findings
- Core purpose: DMARC is designed to protect domains from email spoofing and phishing by instructing receiving mail servers how to handle messages that fail authentication and alignment checks (as stated by Mailjet documentation).
- Prerequisite for DMARC: SPF and DKIM must be properly configured and functioning before DMARC can be effectively implemented, especially for a p=reject policy.
- Reporting functionality: DMARC adds a crucial reporting function (RUA and RUF reports) that provides visibility into email authentication results, which is vital for safe policy enforcement.
- Policy enforcement levels: Documentation outlines three policy levels (p=none, p=quarantine, p=reject), with p=reject offering the highest level of enforcement and protection.
Key considerations
- Gradual progression advised: The transition to p=reject should always be gradual, typically starting with p=none to gather data and identify all legitimate sending sources.
- Alignment requirement: For DMARC to pass, emails must pass SPF or DKIM authentication and pass DMARC alignment, meaning the domain in the From header matches the authenticated domain.
- Reporting analysis: Analyzing DMARC reports is not merely about identifying fraudulent activity but also about uncovering any legitimate email flows that might not be correctly authenticated (as outlined by Mimecast's documentation).
- Policy flexibility: The pct tag allows senders to apply a DMARC policy to only a percentage of their mail, enabling controlled testing of p=quarantine or p=reject before full deployment.
Technical article
Mailgun documentation states that a DMARC policy will instruct Internet Service Providers (ISPs) to reject emails originating from fraudulent IP addresses that are attempting to impersonate your domain, reinforcing the fundamental security purpose of p=reject.
Technical article
DuoCircle documentation highlights that the most effective way to prevent attackers from spoofing your emails is to configure your DMARC policy to p=reject, significantly improving domain security and trust.
Related resources
8 resources
Related pages
How to safely transition your DMARC policy to quarantine or reject
Simple DMARC examples: how to start with a p=none policy
Understanding and troubleshooting DMARC reports from Google and Yahoo
A simple guide to DMARC, SPF, and DKIM
The benefits of implementing DMARC
Email Deliverability Issues: Getting Your Messages to the Inbox in 2025
Why Your Emails Fail: Expert Guide to Improve Email Deliverability [2025]
Why your emails are getting a 'DMARC verification failed' error
List of DMARC tags and their meanings
Boost Email Deliverability Rates: Technical Solutions from Top Performing Senders
