Summary
Setting a DMARC policy of p=reject offers the highest level of protection against email spoofing and is a key requirement for adopting BIMI. This policy instructs recipient servers to block messages that fail DMARC authentication. However, implementing p=reject should be the final stage of a careful, phased DMARC deployment, progressing from p=none to p=quarantine to gather data and test the impact. Thorough and continuous monitoring of DMARC reports is essential at each stage to identify all legitimate email sending sources, including third-party services, and ensure they are properly authenticated with SPF and DKIM to prevent valid emails from being inadvertently blocked.
Key findings
- Strongest Enforcement: DMARC p=reject is the strongest enforcement policy, instructing recipient mail servers to outright block unauthenticated messages that fail DMARC checks, providing the highest level of protection against spoofing and phishing.
- BIMI Requirement: A DMARC policy of p=reject or p=quarantine is required for BIMI (Brand Indicators for Message Identification) to display your brand's logo next to your sender name in supported inboxes.
- Risk of Blocking Legitimate Mail: The primary issue with immediately implementing p=reject is the potential to inadvertently block legitimate email if previously unknown or misconfigured mailstreams are not properly authenticated, leading to delivery failures.
- Varying Receiver Interpretation: Receiver interpretation of DMARC policies can vary; at least one ISP, according to Valimail, treats p=reject and p=quarantine policies exactly the same, by bulk foldering the mail.
Key considerations
- Phased Deployment: Implement DMARC p=reject as the final step in a gradual transition, starting with p=none to gather data, then p=quarantine for testing, and finally p=reject. Avoid rushing to p=reject, especially for complex email environments.
- Monitor DMARC Reports: Continuously analyze DMARC aggregate reports (RUA) throughout all phases. This is crucial for identifying all legitimate email sending sources, including third-party services like marketing platforms, recruiting apps, or help desk software, that use your domain.
- Authenticate All Mailstreams: Before enforcing p=reject, ensure all identified legitimate email streams are properly authenticated with SPF and DKIM and achieve DMARC alignment. Failing to do so can result in legitimate emails being blocked.
- Specialized Knowledge for New Domains: If implementing p=reject on a new domain, particularly one with a complex email system, it requires someone with deep DMARC knowledge to prevent critical failures or an 'apocolycatastrophuck,' though new domains with dedicated ESP use can sometimes accelerate.
- Address Redirection Challenges: Be aware that a p=reject policy can cause issues with mail redirection, particularly for discussion lists, which may impact legitimate message delivery.
- Utilize Monitoring Tools: Leverage tools like Google Postmaster, dmarcian.com, or 250ok.com to monitor DMARC reports effectively, helping to discover unknown mail streams or third-party spoofing attempts.
What email marketers say
16 marketer opinions
Building on a phased approach, implementing a DMARC p=reject policy is the ultimate goal for robust email security, significantly curbing spoofing and phishing attempts by blocking unauthenticated messages. This strong enforcement, while ideal for BIMI alignment and maximum protection, demands meticulous preparation. Senders must be highly confident in their outgoing mail streams, having spent several weeks or months extensively monitoring DMARC reports at p=none and p=quarantine. This crucial period allows for comprehensive identification and proper configuration of all legitimate sending sources, including third-party services like marketing platforms or transactional email providers. Only after ensuring every valid email stream is correctly authenticated and aligned should p=reject be deployed, thus preventing the unintended blocking of important legitimate mail. While a newly dedicated domain might accelerate this process, continuous vigilance through DMARC reporting remains essential to understand all mail flows and ensure successful delivery.
Key opinions
- High Confidence Required: Implementing p=reject necessitates a high degree of confidence in the proper authentication and alignment of all your domain's outgoing mail streams, as unauthenticated legitimate mail will be blocked.
- BIMI Alignment Certainty: While BIMI technically accepts p=quarantine, adopting p=reject provides greater certainty for BIMI alignment and display, given the varying interpretations by email receivers.
- Accelerated Deployment for Dedicated Domains: For domains or subdomains newly set up exclusively for an Email Service Provider, ESP, with no other mail usage, the transition to p=reject can often be accelerated, though ongoing monitoring remains crucial.
Key considerations
- Thorough Phased Approach: Before deploying p=reject, dedicate several weeks or months to thorough monitoring with p=none and careful testing with p=quarantine to ensure comprehensive discovery and proper authentication of all legitimate email sources.
- Identify and Rectify Failed Streams: Actively use DMARC reports during the p=none and p=quarantine phases to identify any legitimate email streams that fail authentication, then promptly configure them with proper SPF and DKIM to achieve DMARC alignment.
- Expertise for Complex Deployments: Implementing p=reject on established or complex domains requires an individual with deep DMARC knowledge and a comprehensive understanding of the organization's entire email ecosystem to avoid critical service disruptions.
- Continuous Monitoring is Paramount: Even after moving to p=reject, maintain continuous monitoring of DMARC reports, using tools like dmarcian.com, 250ok.com, or Google Postmaster, to identify unknown mail streams, third-party spoofing, or any unexpected rejections.
- Beware of Redirection Issues: Be aware that a p=reject policy can potentially cause issues with legitimate mail redirection, especially for discussion lists, which may impact message delivery.
Marketer view
Marketer from Email Geeks explains the meanings of DMARC policies: 'none' for getting a handle on things, 'quarantine' for putting suspected mail in the spam folder, and 'reject' for outright blocking unauthenticated mail. He notes that 'reject' is suitable if you are very confident about your outgoing mail, but also warns that 'p=reject' can cause issues with mail redirection, particularly for discussion lists.
5 Oct 2022 - Email Geeks
Marketer view
Marketer from Email Geeks recommends sticking with p=none for several months to gather feedback reports before moving to a stricter policy. He warns that implementing p=reject on a new domain requires someone with deep DMARC knowledge and a full understanding of the email system to avoid critical failures or an 'apocolycatastrophuck'.
16 Mar 2023 - Email Geeks
What the experts say
4 expert opinions
While DMARC p=reject is a robust policy providing maximum protection against domain spoofing and is essential for displaying brand logos via BIMI, its implementation requires extreme caution. This policy directly instructs receiving servers to reject emails that fail DMARC authentication, making it unsuitable for organizations that have not meticulously prepared. The most significant risk lies in inadvertently blocking legitimate email streams that were previously unknown or improperly authenticated. Therefore, a deliberate, phased approach is paramount, beginning with p=none to gather comprehensive DMARC reports and identify all legitimate sending sources, followed by a transition to p=quarantine to test the policy's impact. Before reaching p=reject, every legitimate email source, including third-party senders, must be properly authenticated with SPF and DKIM and achieve DMARC alignment to avoid severe deliverability issues. It's also important to note that some ISPs may treat p=reject and p=quarantine policies similarly, by simply bulk-foldering mail rather than outright rejecting it.
Key opinions
- Highest Protection: DMARC p=reject is the strongest policy for protecting against spoofing and phishing attacks by enforcing the outright rejection of unauthenticated emails.
- BIMI Requirement: It serves as a critical requirement for enabling BIMI, allowing brand logos to be displayed in supporting email inboxes.
- Risk of Legitimate Mail Rejection: The primary challenge with implementing p=reject is the potential for legitimate, but unauthenticated, mail streams to be blocked, especially those previously unknown to the sender.
- Varying ISP Interpretation: Some email service providers may interpret p=reject and p=quarantine policies similarly, potentially bulk-foldering mail instead of outright rejecting it, as reported by Valimail.
Key considerations
- Phased Implementation is Crucial: Never rush to DMARC p=reject; always follow a gradual, phased approach, starting with p=none to gain visibility into all mailstreams and then p=quarantine for testing the policy's impact.
- Comprehensive DMARC Report Review: Thoroughly review DMARC reports at each stage, particularly during the p=none phase, to identify all legitimate sending sources, including any previously unknown or third-party services, that use your domain.
- Ensure Full Authentication and Alignment: Before moving to p=reject, verify that all legitimate email flows are correctly authenticated with SPF and DKIM and achieve DMARC alignment to prevent legitimate emails from being inadvertently blocked or failing deliverability.
- Assess Organizational Complexity: Organizations with complex email ecosystems and numerous third-party senders must exercise extra caution and allow ample time for preparation and remediation before considering p=reject.
Expert view
Expert from Email Geeks explains that the choice of a DMARC policy, such as p=reject, depends on what the sender hopes to achieve. She confirms that p=reject is required for BIMI. Laura warns that the biggest issue with going to p=reject is discovering previously unknown mailstreams that are not properly authenticated, which could lead to mail being rejected. She strongly advises reviewing DMARC reports to see what is currently failing before implementing any stricter policy. Laura also adds that, according to Valimail, at least one ISP treats p=reject and p=quarantine policies exactly the same, by bulk foldering the mail.
25 Feb 2025 - Email Geeks
Expert view
Expert from Spam Resource explains that DMARC p=reject, while a strong policy against spoofing, is not suitable for all organizations, especially those with complex email ecosystems involving many third-party senders. Rushing to this policy without thorough monitoring and ensuring all legitimate email sources are properly authenticated and aligned can lead to legitimate mail being blocked. It is crucial to use DMARC reports (starting with p=none) to identify and rectify authentication issues across all sending systems before considering p=reject.
30 Mar 2023 - Spam Resource
What the documentation says
4 technical articles
The DMARC p=reject policy is the most robust measure for preventing email spoofing and phishing by instructing recipient mail servers to completely reject messages that fail DMARC checks. While offering the highest level of protection, this powerful policy must be implemented with extreme caution, serving as the final step in a gradual deployment. Organizations should meticulously transition from p=none to p=quarantine, dedicating ample time to monitor DMARC reports. This process ensures all legitimate email sources, including third-party services, are identified, properly configured with SPF and DKIM, and consistently achieve DMARC alignment. Only after verifying that no legitimate mail will be inadvertently blocked should p=reject be enabled.
Key findings
- Highest Enforcement Level: DMARC p=reject is the strongest enforcement policy, instructing recipient mail servers to completely reject messages that fail DMARC checks, providing maximum protection against email spoofing.
- Phased Implementation Essential: Successful deployment of p=reject necessitates a cautious, gradual transition from less stringent policies, specifically p=none and p=quarantine, to prevent inadvertent blocking of legitimate email.
- Requires Full Alignment: Enabling p=reject is only advisable when an organization is highly confident that all legitimate email sources are correctly configured for SPF and DKIM alignment, ensuring proper authentication for all outgoing mail.
- Data-Driven Decision: The decision to move to p=reject should be based on thorough analysis of DMARC reports, confirming that all legitimate mail flows consistently pass authentication and alignment checks.
Key considerations
- Gradual Rollout: Always implement p=reject as the final step in a phased deployment, progressing from p=none to gather data, then p=quarantine for testing, and finally to p=reject for full enforcement.
- Comprehensive Authentication: Before enabling p=reject, ensure all legitimate email sending sources, including third-party services, are correctly configured with SPF and DKIM, achieving DMARC alignment to prevent valid emails from being blocked.
- Diligence with DMARC Reports: Continuously monitor and analyze DMARC reports throughout all deployment phases to identify all legitimate email streams, detect any authentication failures, and ensure full compliance before enforcing p=reject.
- Extensive Testing: Dedicate sufficient time during the p=quarantine phase for extensive testing and analysis of DMARC reports to confirm that legitimate email is not inadvertently blocked, minimizing deliverability risks upon p=reject deployment.
Technical article
Documentation from Google Workspace Admin Help explains that p=reject is the strongest DMARC enforcement policy and should be enabled only after an organization is confident that all legitimate email sources are correctly configured for SPF and DKIM alignment, recommending a cautious transition from p=none and p=quarantine while monitoring DMARC reports.
7 Jun 2024 - Google Workspace Admin Help
Technical article
Documentation from Microsoft Learn shares that p=reject instructs recipient mail servers to completely reject messages failing DMARC checks, and this policy should be implemented gradually, moving from p=none to p=quarantine and finally to p=reject, only after extensive testing and analysis of DMARC reports ensure no legitimate email is inadvertently blocked.
22 Nov 2023 - Microsoft Learn
How should I configure DMARC for multiple domains and when should I implement a reject policy?
How to implement DMARC p=reject policy safely, especially when using ESPs like Mailchimp and GetResponse?
How to implement DMARC p=reject policy safely to avoid email deliverability issues?
What are the best practices for implementing a DMARC policy, and should you use reject or quarantine?
What DMARC settings should I use and what are the implications of using p=reject?
When should you use DMARC p=none, p=quarantine, or p=reject policies?
