Why am I receiving DMARC failure reports when my email authentication seems correct?
Michael Ko
Co-founder & CEO, Suped
Published 5 Jun 2025
Updated 16 Aug 2025
7 min read
It can be confusing, even frustrating, when DMARC failure reports land in your inbox, especially when you're confident that your SPF and DKIM records are correctly configured and passing. You've done the diligent work of setting up email authentication, yet these reports suggest something is amiss. This scenario is far more common than you might think and doesn't always point to a flaw in your core authentication setup. Instead, it often highlights nuances in how email flows through the internet, particularly with forwarding or complex sending environments.
Understanding these reports requires a deeper dive into how DMARC works alongside SPF and DKIM, focusing specifically on a concept called alignment. DMARC's primary goal is to ensure that the domain visible to the recipient (the 'From' header domain) matches the domain that passed either SPF or DKIM. If this alignment fails, even if SPF or DKIM technically passed on their own, the DMARC check can still result in a 'fail'.
These seemingly contradictory reports are actually valuable. They provide insights into legitimate email streams that might be encountering issues or reveal attempts at spoofing your domain. The key is knowing how to interpret them correctly. Let's explore the common culprits behind DMARC failures when your authentication appears to be in order.
DMARC reports often highlight an issue with alignment. SPF, DKIM, and DMARC each authenticate different aspects of an email, but DMARC is unique because it also verifies that the domain in the "From" header (the one users see) aligns with the domains checked by SPF or DKIM. If this alignment is broken, the email will fail DMARC, even if SPF or DKIM individually pass.
Alignment comes in two forms: relaxed and strict. Relaxed alignment allows subdomains to align with the organizational domain, while strict alignment demands an exact match. For instance, if your SPF passes for m.yourdomain.com and your "From" header is yourdomain.com, it will pass SPF alignment under a relaxed policy but fail under a strict policy.
Many email service providers (ESPs) or third-party senders, when sending email on your behalf, may use their own domains in the Return-Path (for SPF) or DKIM signing domain. If these domains do not align with your "From" header domain, DMARC will fail. This is a common source of unexpected failures, where your email is legitimate, but the technical alignment required by DMARC is not met. If you are experiencing this, you can learn how to debug DMARC authentication failure and alignment issues.
Strict DMARC alignment
Requires the "From" header domain to precisely match the domain that passed SPF or DKIM. For example, if your SPF record is for mail.example.com, your "From" header must also be mail.example.com.
Pros: Offers the highest level of protection against email spoofing (impersonation).
Cons: Can be challenging to implement, especially with third-party senders or complex mail flows.
Common causes of DMARC failures
One of the most frequent reasons for DMARC failures, despite seemingly correct authentication, is email forwarding. When an email is forwarded, it often passes through an intermediary server that may alter the message. This alteration can break the original SPF or DKIM signatures.
For instance, SPF checks the IP address of the sending server. When an email is forwarded, the forwarding server becomes the new sender, and its IP address won't match the original domain's SPF record, leading to an SPF failure. Similarly, DKIM signs parts of the email header and body. If a forwarding server modifies a signed part of the email, the DKIM signature will no longer be valid, causing a DKIM failure. If either of these break, DMARC will fail due to a lack of alignment. This is why you might receive a DMARC failure report when authentication seems correct.
Another common scenario involves third-party sending services. Many organizations use external platforms for marketing, transactional, or customer service emails. While these services usually support SPF and DKIM, they might not always ensure proper DMARC alignment by default. For example, some services might send emails with a Return-Path (SPF) or DKIM signing domain that is different from your "From" header domain, leading to DMARC failure.
DNS misconfigurations, though seemingly minor, can also trigger DMARC failures. These include expired DKIM keys, incorrect DNS record entries, or exceeding the SPF lookup limit. Even if a record was once correct, changes to your sending infrastructure or DNS provider can inadvertently break it. It's crucial to regularly check your DMARC setup and other authentication records to ensure they are up-to-date and correctly formatted.
Email forwarding
When an email is forwarded, the intermediary server's IP address replaces the original sender's in the mail path. This causes the SPF check to fail because the forwarding server's IP is not authorized by the original domain's SPF record. DKIM can also break if the message content is altered during forwarding.
Third-party senders
Many email marketing or transactional services use their own domains for SPF (Return-Path) or DKIM signing. While this passes their authentication, it might not align with your "From" header domain, causing DMARC to fail. This is a common cause of legitimate DMARC failure reports.
Interpreting DMARC failure reports
DMARC reports are designed to give you visibility into how your domain's emails are performing against authentication checks. There are two main types: aggregate (RUA) and forensic (RUF). Aggregate reports (the ones you're likely receiving) summarize daily authentication results, showing passes and failures, and the sources of traffic.
A key point from the DMARC specification is that a "DMARC fail" in a report doesn't necessarily mean your DMARC record is incorrect or that the email was blocked. It simply means that the email failed to satisfy your DMARC policy's alignment requirements. If your policy is p=none, the email will still be delivered, but the report will show the failure. You can learn more about how DMARC works with SPF and DKIM in this guide to DMARC.
When analyzing these reports, pay close attention to the source IP addresses. If you see failures originating from IPs not directly controlled by you or your legitimate sending services, it could indicate forwarding or even spoofing attempts. Microsoft (including Outlook) is a common sender of DMARC failure reports related to forwarding, so seeing their IP in a report often points to this scenario.
These reports are a cornerstone of DMARC's utility. They allow you to diagnose DMARC failures and gain full visibility into your email ecosystem. By regularly reviewing them, you can identify sources of unauthenticated email, whether legitimate or malicious, and take appropriate action to improve your domain's email security posture.
Example DMARC report snippet
ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass (sender ip is 18.214.133.205) smtp.rcpttodomain=example.com smtp.mailfrom=yourdomain.com; dmarc=none; dkim=fail (signature did not verify) header.d=yourdomain.com; arc=none (0)
Refining your DMARC strategy
Receiving DMARC failure reports when your SPF and DKIM seem correct is often a sign of misaligned domains or email forwarding, rather than a fundamental flaw in your authentication setup. It's important to understand the role of DMARC alignment and how common email flow patterns, like forwarding or third-party sending, can impact these checks.
These reports, though alarming at first glance, are invaluable tools for gaining visibility into your email traffic. They allow you to pinpoint the exact reasons for authentication failures and take corrective action, ultimately strengthening your email security and deliverability. Don't simply dismiss these reports, use them as an opportunity to further refine your email authentication strategy.
Views from the trenches
Best practices
Always aim for DMARC alignment for both SPF and DKIM. This means the domain in your "From" header should match the SPF aligned domain (Return-Path) or the DKIM signing domain.
Regularly monitor your DMARC aggregate reports to identify trends and unexpected sources of email traffic, whether legitimate or unauthorized.
Work closely with your third-party email senders to ensure they support DMARC alignment and configure their settings correctly for your domain.
Start with a DMARC policy of p=none (monitor only) to collect reports and understand your email ecosystem before moving to more restrictive policies like quarantine or reject.
Implement DMARC for all sending domains, including those not actively sending email, to prevent them from being spoofed by malicious actors.
Common pitfalls
Assuming SPF or DKIM passing means DMARC will also pass. Alignment is a separate, critical check.
Ignoring DMARC reports, especially those indicating failures, as they provide crucial insights into deliverability and potential spoofing.
Setting a DMARC policy of p=quarantine or p=reject without thoroughly analyzing reports, which can lead to legitimate emails being blocked.
Not accounting for email forwarding, which commonly breaks SPF and DKIM authentication, leading to DMARC failures.
Using generic DMARC records or those provided by a third-party without customizing them for your specific sending infrastructure.
Expert tips
Focus on domain alignment first, then address any technical issues related to SPF or DKIM passing. The DMARC check relies on both passing and aligning.
Leverage DMARC forensic reports (RUF) if available, as they provide more detailed information about individual failed emails, helping pinpoint specific issues.
For large organizations, segmenting email sending by subdomain can help manage DMARC policies more granularly and isolate potential issues.
If using a third-party sender, request their specific DMARC alignment instructions or verify how they handle the "From" header and authentication domains.
Be aware that some legitimate email flows, like mailing lists or certain forwarding scenarios, may inherently fail DMARC. These should be identified and understood.
Expert view
Expert from Email Geeks says that if an SPF record shows as permitted, but DKIM fails, DMARC should still pass due to alignment if the domains align.
2023-04-15 - Email Geeks
Marketer view
Marketer from Email Geeks says that a DMARC failure report can be generated even when the DMARC policy is set to 'none' for monitoring purposes.
