What are common confusions in email authentication and DMARC reporting?
Matthew Whittaker
Co-founder & CTO, Suped
Published 1 Aug 2025
Updated 17 Aug 2025
6 min read
Email authentication protocols like SPF, DKIM, and DMARC are fundamental to securing email communication and ensuring deliverability. While designed to prevent spoofing and phishing, their implementation and interpretation can often lead to significant confusion. Many organizations struggle to fully grasp the nuances, leading to errors that impact their email sending reputation and inbox placement.
The complexity often arises from the interplay between these standards, particularly with DMARC, which ties SPF and DKIM together. Understanding how to correctly configure them and, more importantly, how to interpret the feedback from DMARC reports is crucial for effective email security.
One of the most frequent sources of confusion is distinguishing between a successful SPF or DKIM authentication and a successful DMARC alignment. An email can technically pass its SPF or DKIM checks, yet still fail DMARC because it doesn't meet the alignment requirement.
SPF (Sender Policy Framework) verifies the sending IP address against a published list in the domain's DNS. DKIM (DomainKeys Identified Mail) uses a cryptographic signature to verify that the email content hasn't been tampered with and that it originated from a legitimate sender. However, DMARC (Domain-based Message Authentication, Reporting, and Conformance) adds an additional layer: alignment. This means the domain in the From header (the one users see) must match the domain used for SPF or DKIM validation. If the domains don't align, the email fails DMARC, even if SPF or DKIM technically pass separately.
This distinction often leads to questions like, Why does DMARC authentication fail when SPF and DKIM pass and how can it be fixed? It highlights that passing authentication is only half the battle. Achieving proper alignment is what truly secures your domain under DMARC.
Authentication pass
SPF pass: The email originated from an IP address authorized in the SPF record.
DKIM pass: The email's digital signature is valid and matches the public key in DNS.
No alignment check: These protocols do not inherently require the From header domain to match the authenticated domain.
DMARC alignment pass
SPF alignment: The From header domain matches the Return-Path domain used for SPF validation (strict or relaxed).
DKIM alignment: The From header domain matches the domain in the DKIM signature (strict or relaxed).
DMARC pass: At least one of the aligned SPF or DKIM checks passes.
Decoding DMARC policies and actions
DMARC policies, indicated by the p tag in your DMARC record, instruct receiving mail servers on how to handle emails that fail DMARC checks. The options are p=none, p=quarantine, and p=reject. The confusion often stems from when and how to transition between these policies.
Starting with p=none is advised to gain visibility into your email ecosystem without impacting deliverability. However, many remain at this policy level indefinitely, missing out on the full protective benefits of DMARC. Moving to p=quarantine or p=reject too quickly, or without thoroughly analyzing DMARC reports, can lead to legitimate emails being sent to spam or blocked altogether. This is a primary concern for those asking How to safely transition your DMARC policy to quarantine or reject.
Another area of policy-related confusion revolves around subdomains. A DMARC record published at the organizational domain typically applies to all its subdomains unless explicitly overridden. Misunderstanding this can leave subdomains vulnerable or unintentionally block legitimate email flows.
Best practices for policy transition
Start with p=none: Monitor reports without affecting email delivery.
Gradual move: Once comfortable with the data, incrementally increase the percentage of emails to apply p=quarantine, then p=reject.
Subdomain consideration: Ensure policies are explicitly set for subdomains if they differ from the organizational domain.
Interpreting DMARC reports
DMARC reports (both aggregate RUA and forensic RUF) are the backbone of DMARC implementation, providing data on who is sending email using your domain. However, these XML-formatted reports are notoriously difficult to parse and interpret manually. This often leads to confusion, particularly when trying to interpret DMARC reports for unrecognized email sending sources or low volume failures.
You'll see data points like source IP, SPF and DKIM authentication results, and their respective alignment statuses. The challenge lies in distinguishing legitimate sending services that might be misconfigured from actual malicious activity. Many find it hard to reconcile why seemingly legitimate emails might appear as failing DMARC in these reports.
To effectively use these reports, you need tools or expertise to automate parsing and visualize the data. This helps identify unauthorized senders, troubleshoot authentication issues, and assess the impact of your DMARC policy. More information on this topic can be found in a detailed guide to DMARC aggregate reports.
Indicates whether the From header domain aligned with the authenticated SPF or DKIM domain.
Pass, Fail
Count
The number of emails sent from that source with those results.
100
Common pitfalls and troubleshooting
Even with a seemingly perfect DMARC setup, legitimate emails can still fail. One of the most common culprits is email forwarding. When an email is forwarded, the Return-Path (used for SPF) often changes to the forwarding server's domain, breaking SPF alignment. Similarly, DKIM signatures can be invalidated if the email content is modified during forwarding, leading to DMARC failures. This scenario is a frequent concern when asking How do email forwarding and DMARC policies affect email delivery and reporting?
Other common pitfalls include DNS misconfigurations, such as incorrect SPF syntax, exceeding the 10-DNS-lookup limit for SPF records, or having multiple SPF records for a single domain. DKIM issues might involve incorrect selector names or public keys not matching the private keys used for signing. These subtle errors can cause DMARC failures, making it difficult to troubleshoot DMARC failures and their impact on email deliverability.
These issues often lead to frustration, as legitimate emails from trusted services might suddenly land in spam or be rejected. Understanding the nuances of how DMARC interacts with SPF and DKIM, and recognizing common failure points, is key to diagnosing and resolving these problems efficiently. For a comprehensive overview, refer to Cloudflare's guide on DMARC, DKIM, and SPF.
Common reasons for DMARC failure
Email forwarding: Can break SPF and DKIM alignment.
Third-party senders: Services not properly configured to align with your domain.
Subdomain issues: DMARC policies not correctly applied or overridden for subdomains.
Views from the trenches
Best practices
Regularly review your DMARC aggregate reports to identify all legitimate sending sources for your domain, even the low volume ones.
Ensure that all third-party email sending services are properly configured to send mail on behalf of your domain, correctly aligning SPF and DKIM.
When transitioning DMARC policies, proceed slowly and incrementally, starting with p=none, then moving to quarantine, and finally reject.
Common pitfalls
Conflating SPF and DKIM authentication passes with DMARC alignment passes, leading to a misunderstanding of email deliverability issues.
Ignoring DMARC reports or failing to consistently analyze them, which means missing critical insights into email spoofing and misconfigurations.
Implementing a p=reject DMARC policy too aggressively without proper monitoring, causing legitimate emails to be blocked.
Expert tips
Understand the difference between DMARC 'pass' and 'alignment' to accurately diagnose email authentication issues and improve deliverability.
Leverage DMARC reporting tools to simplify the analysis of complex XML reports and gain clearer visibility into your email traffic.
Pay close attention to how email forwarding impacts SPF and DKIM authentication, as it's a frequent cause of DMARC failures for legitimate emails.
Expert view
An expert from Email Geeks says DMARC authentication can pass when SPF and DKIM pass headers, but it's likely not passing alignment, which is what DMARC truly requires.
2024-02-09 - Email Geeks
Expert view
An expert from Email Geeks says DMARC reporting can be confusing, particularly the 'evaluated' section, even for those familiar with email protocols.
2024-02-09 - Email Geeks
Achieving DMARC clarity
Navigating the complexities of email authentication and DMARC reporting is essential for maintaining strong email security and deliverability. The key lies in understanding the core concepts of SPF, DKIM, and DMARC alignment, rather than just basic authentication passes.
By diligently monitoring DMARC reports, carefully transitioning policies, and addressing common pitfalls like email forwarding and DNS errors, organizations can significantly improve their email deliverability and protect their brand from impersonation and phishing attacks. It's a continuous process that requires ongoing attention and adjustment.
