Summary
When a DMARC policy is set to a level higher than p=none (such as p=quarantine or p=reject), the primary goal is to enhance email security and combat spoofing. However, it's a common concern that this stricter enforcement might inadvertently block legitimate emails. This occurs when emails that should pass authentication fail due to various reasons, leading to them being quarantined or rejected by receiving mail servers.
Key findings
- Authentication failures: Legitimate emails can be blocked if their SPF or DKIM authentication fails, even if the sender is authorized. These failures could be due to misconfigurations in the sender's email service provider (ESP), customer relationship management (CRM) system, or other email platforms.
- Email forwarding issues: Some email forwarding services can alter headers or content, which may break DKIM signatures and cause DMARC authentication to fail. This is a common, albeit low-volume, cause of legitimate mail being blocked.
- Reputation anchoring: DMARC helps mailbox providers (MBPs) confidently anchor sender reputation to an authenticated identity. If a domain has a poor reputation for other best practices, even DMARC-passing emails might be blocked based on past sending behavior.
- Rogue sending: Unauthorized departments or individuals within an organization might use unauthenticated services to send emails from the domain, causing these legitimate (but unaligned) emails to fail DMARC checks.
- Network and DNS issues: While minimal, temporary network problems or DNS lookup failures can prevent successful authentication, leading to DMARC failures and subsequent blocking.
Key considerations
- Pre-enforcement monitoring: Before moving to an enforced DMARC policy, it's crucial to monitor DMARC reports (RUA and RUF) at p=none to identify and fix all legitimate sending sources that might not be DMARC aligned.
- Addressing misconfigurations: Correctly configuring SPF and DKIM for all email sending services is paramount. This ensures that your legitimate emails pass authentication checks before they even reach the DMARC policy evaluation stage. If you're encountering issues, refer to our guide on why some emails fail DMARC checks.
- Understanding DMARC's role: DMARC itself doesn't cause blocking if emails are properly authenticated. Instead, it provides a framework for MBPs to act confidently on the authentication status. If a legitimate email is blocked despite passing DMARC, the root cause often lies in broader sender reputation or content issues. More information can be found on understanding DMARC policies.
What email marketers say
Email marketers often express concern about the immediate impact of moving to a DMARC policy stronger than p=none. The general sentiment is that if proper authentication is in place and rogue sending is minimized, the transition should be smooth, with legitimate emails remaining unaffected. Any blocking observed would typically highlight existing authentication issues or unauthorized sending practices that need to be addressed.
Key opinions
- Desired blocking: Marketers recognize that if DMARC causes blocking, it's either because the email is spoofing, or it's an alert to fix SPF or DKIM configurations, which are both beneficial outcomes.
- Proactive management: If DMARC reports have been diligently managed while at p=none, legitimate emails should not experience deliverability issues when moving to p=quarantine or p=reject.
- Addressing rogue sending: Rogue sending (e.g., unauthorized Mailchimp accounts) is a common cause of DMARC failures for otherwise legitimate mail, and marketers agree that such practices should be stopped or properly authenticated.
- No noticeable impact (ideal scenario): The ideal scenario for marketers is that transitioning to a stronger DMARC policy like p=quarantine with pct=100 would go unnoticed by legitimate senders, as all their emails are already authenticated correctly. This aligns with our guidance on implementing DMARC p=reject safely.
Key considerations
- Understanding DMARC failures: Marketers need to understand that DMARC failures for legitimate emails indicate a problem with authentication, not the DMARC policy itself. It serves as an alert to fix underlying issues.
- Managing internal sending sources: It's essential to identify and manage all internal sending sources that use your domain to ensure they are properly authenticated. This prevents legitimate emails from being blocked due to rogue sending.
- Impact of policy changes: While the internet might not explicitly state a smooth transition, careful monitoring and remediation during a p=reject or p=quarantine deployment should minimize unexpected blocking.
- Continuous monitoring: Even after implementing a stricter policy, ongoing DMARC report analysis is vital to catch any new authentication issues or rogue sending attempts. DuoCircle also provides insights on DMARC enforcement.
Marketer view
Marketer from Email Geeks expresses curiosity about legitimate emails being blocked when DMARC policy is higher than p=none. They understand that enforcement helps deter spoofers, but wonder why it would also create difficulties for legitimate senders.
Marketer view
Marketer from Spiceworks Community notes that spoofed emails sometimes fail DMARC, DKIM, and SPF checks but still get delivered to the inbox, indicating that DMARC enforcement isn't always absolute, or other factors are at play.
What the experts say
Experts agree that if legitimate emails are blocked when DMARC is enforced, the issue typically stems from underlying authentication problems, not the DMARC policy itself. They highlight common pitfalls like misconfigurations, email forwarding complexities, and the importance of DMARC in providing a robust foundation for reputation assessment by mailbox providers. While edge cases exist, proper setup and monitoring usually prevent unintended blocking.
Key opinions
- Authentication failures are key: Experts emphasize that DMARC failures and subsequent rejections at p=reject are directly caused by underlying authentication failures (SPF or DKIM), often due to misconfigurations or spoofing.
- DMARC for reputation: Authentication via DMARC enables mailbox providers to assign and anchor reputation to the authenticated identity, meaning that DMARC passes allow for confident blocking based on a sender's history of poor practices.
- Edge cases exist: While rare, random weird stuff like email forwarding rewriting headers can break DKIM signatures and cause legitimate emails to fail DMARC. Also, network problems leading to authentication failures should be minimal.
- Pct tag inconsistency: The implementation of the 'pct' (percentage) tag in DMARC policies is not consistent across all mailbox providers and may even be ignored. There is momentum to remove it in future DMARC specifications.
Key considerations
- Prioritize proper authentication: The primary focus should be on ensuring all legitimate sending sources (including ESPs, CRMs, and internal systems) are correctly authenticating with SPF and DKIM. This is fundamental to prevent DMARC failures and deliverability issues, as explained in our simple guide to DMARC, SPF, and DKIM.
- Distinguishing DMARC's role: It's crucial to understand that if DMARC passes but an email is still blocked, the blocking is likely due to other reputation factors, not DMARC itself. DMARC simply confirms the sender's identity, allowing the MBP to apply its filters confidently.
- Handling forwarding: While challenging to control external forwarding, awareness of its potential to break DMARC alignment is important for troubleshooting. Some platforms, like Outlook, may not handle forwarded invites in a DMARC-friendly manner, leading to failures.
- Iterative enforcement: Moving to enforcement policies (p=quarantine or p=reject) should ideally be done after thorough monitoring at p=none to minimize surprises. This aligns with advice on safely transitioning DMARC policy. Mailgun also provides a guide on implementing DMARC.
Expert view
Expert from Email Geeks states that authentication failures cause DMARC failures, which in turn lead to rejections when a policy is set to p=reject. This includes issues like spoofing, misconfigured SPF/DKIM in ESPs, or email forwarding that breaks signatures.
Expert view
Expert from Spam Resource explains that DMARC works by establishing whether an email's 'From' domain aligns with its authenticated SPF or DKIM domains. If this alignment fails and the policy is set to quarantine or reject, the email will be treated accordingly.
What the documentation says
DMARC documentation outlines specific rules for how receiving mail servers should treat emails that fail authentication based on the published DMARC policy. While the goal is to filter out fraudulent messages, legitimate emails can be affected if they do not meet the authentication requirements, which include SPF and DKIM alignment. The documentation also touches on optional tags like 'pct' and their intended, though sometimes inconsistently applied, behavior.
Key findings
- Policy definitions: The DMARC policy tags, namely p=none, p=quarantine, and p=reject, define the actions receiving servers should take when an email fails DMARC authentication and alignment.
- Authentication standards: DMARC relies on the successful authentication and alignment of both SPF and DKIM records. A failure in either can lead to a DMARC failure.
- Pct tag behavior: The 'pct' tag is intended to allow for a percentage of emails to be subjected to the DMARC policy, enabling a gradual rollout. However, its implementation can vary among different mail providers, and it is not always honored consistently.
- Reporting mechanisms: DMARC includes reporting mechanisms (RUA for aggregate reports and RUF for forensic reports) that provide insight into email authentication results, which are crucial for identifying legitimate emails that might be failing.
Key considerations
- Strictness vs. Deliverability: While stricter DMARC policies like p=reject offer the highest level of protection against spoofing, they also carry the highest risk of blocking legitimate emails if authentication is not perfectly configured across all sending sources. This is why a phased approach is recommended.
- Alignment is critical: Beyond just passing SPF and DKIM, DMARC requires alignment between the RFC5322.From domain and the domains used for SPF or DKIM authentication. Misalignment is a frequent cause of legitimate email DMARC failures. For more details, consult articles on DMARC policy.
- Monitoring reports: Documentation consistently emphasizes the necessity of DMARC report analysis (RUA and RUF). These reports are the primary tools for understanding why legitimate emails might be failing authentication and for identifying all authorized sending sources. Our list of DMARC tags can further assist.
Technical article
Documentation from the DMARC specification states that the purpose of DMARC is to improve and monitor the protection of the domain against fraudulent email. It defines how receiving mail servers should handle unauthenticated emails purporting to be from a protected domain.
Technical article
Documentation from the DMARC.org site clarifies that a p=none policy allows domain owners to collect feedback about email streams without affecting existing mail delivery. This is crucial for initial deployment and identifying legitimate unaligned sources.
Related resources
11 resources
Related pages
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