Summary
Rolling out DMARC enforcement, particularly a strict p=reject policy, requires careful consideration of how email forwarding and potential DKIM issues can impact deliverability. While DMARC is vital for preventing email spoofing and brand impersonation, its implementation can inadvertently block legitimate emails if not managed properly. The core challenge often lies in the nature of email forwarding, which can break SPF and sometimes DKIM alignment, leading to DMARC failures for otherwise valid messages. Addressing underlying DKIM configuration problems and understanding DMARC reports are crucial steps for a successful and safe deployment.
Key findings
- Forwarding impact: Automatic email forwarding frequently causes SPF alignment to break, leading to DMARC failures. This is a design characteristic of DMARC.
- DKIM's role: Proper DKIM implementation, including custom DKIM signatures for services like Google Workspace and all alias domains, is essential to ensure DMARC passes, even when SPF alignment is broken by forwarding.
- ARC protocol: The Authenticated Received Chain (ARC) protocol can mitigate forwarding risks, but its effectiveness is limited to messages forwarded between ARC-aware and mutually trusting mailbox providers.
- Phased rollout: A gradual, phased approach to DMARC enforcement, starting with a p=none policy and slowly moving to p=quarantine and then p=reject, is widely recommended to avoid unintended email rejection.
Key considerations
- Report monitoring: Thoroughly analyze DMARC aggregate reports to identify all legitimate sending sources, especially those failing authentication due to forwarding or misconfiguration.
- Source identification: Before moving to enforcement, identify and ensure DMARC compliance for all internal and third-party email sending sources for your domain.
- DKIM issues first: Prioritize fixing any existing DKIM alignment issues across all domains and subdomains before increasing DMARC policy strictness.
- Forwarded email risk: Understand that DMARC enforcement, particularly p=reject, will likely cause some legitimate forwarded emails to be rejected. A gradual approach provides time to identify and mitigate these issues, as outlined by DuoCircle.
What email marketers say
Email marketers often approach DMARC enforcement with a mix of urgency due to spoofing concerns and trepidation regarding potential deliverability impacts. The complexity of DMARC reports, especially in identifying unrecognized or failing sources, can be a significant hurdle. Marketers typically prioritize protecting their brand from impersonation but are equally concerned about inadvertently blocking legitimate communications, particularly those involving forwarding or third-party services.
Key opinions
- Report complexity: Many marketers find the volume and detail of DMARC reports overwhelming, making it difficult to pinpoint issues or unknown sending sources.
- Spoofing motivation: A primary driver for DMARC enforcement among marketers is the desire to combat email spoofing and prevent their domain from being used for malicious purposes, especially after experiencing automated replies or bounces for un-sent emails.
- Gradual adoption: There's a strong preference among marketers for a cautious, phased rollout of DMARC policies, starting with monitoring before moving to quarantine or reject.
- Third-party services: Concerns exist about how DMARC enforcement impacts emails sent via legitimate third-party services and whether these will properly align and pass DMARC.
Key considerations
- Comprehensive audit: Marketers must conduct a thorough audit to identify all email sending sources (both internal and external vendors) before moving to an enforcing DMARC policy. Mailgun's insights also highlight the importance of a comprehensive audit.
- Forwarding impact assessment: Evaluate the potential impact of DMARC enforcement on legitimate forwarded emails, recognizing that some may be rejected.
- Deliverability focus: While security is key, marketers need to ensure DMARC implementation does not negatively affect overall email deliverability for their campaigns.
Marketer view
A marketer from Email Geeks inquired about the legitimacy of unknown email sources in DMARC reports and whether it's appropriate to contact them directly for clarification. They had a client showing a large volume of emails from bounce.globalrelay.com without a known integration.
Marketer view
A marketer from Email Geeks asked if it's safe to enable DMARC enforcement, specifically concerning Google Calendar invites, which they observed consistently breaking DMARC. They wanted to know if a quarantine or reject policy would negatively impact these emails.
What the experts say
Experts in email deliverability and security emphasize that DMARC's design inherently leads to failures when emails are automatically forwarded due to changes that break SPF and DKIM alignment. They stress the critical role of custom DKIM signatures and thorough infrastructure analysis to ensure proper authentication. While DMARC is a powerful tool against spoofing, experts advocate for a careful, iterative rollout process to avoid unintended blocking of legitimate mail, with a strong focus on resolving underlying authentication issues first.
Key opinions
- Inherent forwarding failure: Experts confirm that DMARC, by its fundamental design, will fail if a message is automatically forwarded (breaking SPF alignment) and potentially modified (breaking DKIM alignment). This is an expected behavior that senders must accept when deploying DMARC.
- Custom DKIM necessity: The absence of a custom DKIM signing domain (e.g., seeing gappssmtp.com) is a significant factor in DMARC failures, highlighting the need for proper DKIM setup for all domains and aliases.
- ARC's limitations: The ARC protocol can help mitigate forwarding risks, but it is implemented by mailbox providers, not senders, and only functions between ARC-aware providers that trust each other.
- Phased enforcement is key: Experts strongly recommend against direct enforcement to a reject policy. Instead, they advise starting with p=quarantine and monitoring reports for several weeks before moving to a stricter policy.
Key considerations
- Prioritize DKIM fixes: Focus on resolving all DKIM configuration issues first, as they are a major cause of DMARC failures, including those related to Non-Delivery Reports (NDRs) and forwarded messages. For further assistance, refer to GoDMARC's advice on ensuring DMARC compliance with email forwarding.
- Deep infrastructure analysis: A thorough analysis of the overall email infrastructure and DMARC report data is essential before making policy changes. This includes reviewing XML details for failed emails to investigate issues in-depth.
- Alias domain checks: Carefully check for any alias or subdomain alias domains in use and ensure DKIM is properly implemented for them to prevent DMARC failures. Suped offers guidance on troubleshooting DMARC failures.
- Spoofing vs. filters: Remember that while DMARC combats spoofing, email filters operate independently and can still block spoofed messages even without DMARC enforcement.
Expert view
An expert from Email Geeks states that most unknown sources in DMARC reports are legitimate forwarding, which by its nature breaks SPF alignment and potentially DKIM alignment during the process.
Expert view
A deliverability expert from SpamResource recommends auditing all email sending services and associated domains thoroughly before attempting to implement DMARC enforcement, emphasizing that this preliminary step is crucial.
What the documentation says
Official documentation and guides on DMARC consistently emphasize a structured, cautious approach to enforcement. They highlight that DMARC builds upon foundational authentication protocols like SPF and DKIM, requiring their proper configuration and alignment. The general consensus from technical documentation is that a phased rollout, starting with monitoring, is critical to prevent unintended email delivery disruptions, especially in the face of challenges posed by email forwarding and potential DKIM misconfigurations.
Key findings
- Prerequisites: DMARC requires SPF and/or DKIM to be properly set up and aligned with the From: domain to function correctly.
- Gradual enforcement: Documentation universally recommends a gradual, phased approach (p=none, then p=quarantine, then p=reject) to allow for monitoring and issue resolution.
- DMARC reports: Accessing and analyzing DMARC aggregate and forensic reports is crucial for identifying all legitimate sending sources and troubleshooting authentication failures before moving to stricter policies.
- Policy impact: Each DMARC policy (none, quarantine, reject) has a distinct impact on how receiving mail servers handle unauthenticated messages, from monitoring to outright rejection.
Key considerations
- Alignment types: Understanding both 'relaxed' and 'strict' alignment modes for SPF and DKIM is important, as they dictate how closely the authenticating domain must match the From: header domain. Details on DMARC tags can further clarify this.
- Email forwarding: Documentation acknowledges that email forwarding can inherently break SPF alignment. Organizations must account for this when considering DMARC enforcement.
- Subdomain policies: It is crucial to consider DMARC policies for subdomains, as they inherit the organizational domain's policy unless explicitly overridden. Read more about safely transitioning DMARC policies.
- Phishing prevention: The primary benefit of DMARC enforcement is to protect against phishing and spoofing, ensuring that invalid DMARC records do not lead to security vulnerabilities, as highlighted by DuoCircle documentation.
Technical article
DuoCircle documentation states that invalid DMARC records fail to effectively filter out phishing and spoofing emails, underscoring the critical need to ensure SPF and DKIM settings are correctly configured and aligned for optimal email security.
Technical article
Mailgun's DMARC guide emphasizes that SPF and DKIM must be fully activated for a domain as a prerequisite for DMARC implementation, and these protocols must be aligned to ensure DMARC can function effectively.
Related resources
13 resources
Related pages
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