If DMARC passes but SPF fails, what are the concerns and impacts on email deliverability?
Michael Ko
Co-founder & CEO, Suped
Published 15 Jul 2025
Updated 16 Aug 2025
7 min read
Email authentication protocols like SPF, DKIM, and DMARC are crucial for ensuring your messages reach the inbox. They act as trust signals, helping mailbox providers distinguish legitimate emails from spam and phishing attempts. Ideally, all three should pass and align for optimal deliverability and domain reputation.
However, you might encounter a scenario where an email passes DMARC authentication, but SPF (Sender Policy Framework) fails. This often happens when DKIM (DomainKeys Identified Mail) successfully authenticates and aligns, satisfying DMARC's requirement for at least one of the two mechanisms to pass with alignment.
The immediate question that arises is, if DMARC passes, are there still concerns or negative impacts on email deliverability when SPF is failing? While a DMARC pass is a strong indicator of legitimacy, understanding the nuances of an SPF failure, even in this context, is important for maintaining a robust email sending infrastructure.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) is designed to give domain owners control over how their emails are handled if they fail authentication checks. For an email to pass DMARC, it needs to pass either SPF or DKIM, and importantly, achieve alignment with the "From" domain visible to the recipient. This means that even if SPF fails, a successful DKIM authentication and alignment can lead to a DMARC pass.
SPF verifies the sending server's IP address against a list of authorized IPs in your domain's DNS record. SPF alignment, specifically "strict alignment," requires the "MAIL FROM" domain (also known as the Return-Path or Envelope From) to exactly match the "From" header domain. DKIM, on the other hand, uses cryptographic signatures to verify that the email content has not been tampered with in transit and that it originates from an authorized domain. DKIM alignment checks if the "d=" tag in the DKIM signature aligns with the "From" header domain.
When DKIM passes and aligns, it often suffices for DMARC, even if SPF fails. This is because DMARC only requires one of the underlying authentication methods to pass and align. Mailbox providers like Google and others use DMARC to determine policy application, and if DMARC passes, the email is generally considered legitimate for delivery, regardless of an SPF-specific failure.
Why SPF might fail even when DKIM passes
One of the most common reasons SPF might fail while DKIM still passes is email forwarding. When an email is forwarded, the forwarding server often changes the "MAIL FROM" address, or the IP address from which the email originates, to its own. This breaks the SPF check because the original sending IP is no longer the one connected to the mail server. However, DKIM's cryptographic signature, attached to the email header, typically remains intact across forwarding, allowing it to still validate successfully.
Another scenario involves sending services that control the SPF domain (e.g., using their own subdomain in the Return-Path) but allow you to use your custom DKIM keys aligned with your main domain. In such cases, SPF may fail to align, but DKIM will pass and align, leading to a DMARC pass. This is a deliberate configuration by some email service providers. You can learn more about how SPF authentication works and fails in these contexts.
Beyond forwarding, technical misconfigurations, such as exceeding the SPF DNS lookup limit (10 DNS lookups), or simply not including all legitimate sending IPs in your SPF record, can cause SPF failures. However, if DKIM is correctly set up for all your sending sources, it can act as a fallback, ensuring DMARC passes and preventing immediate delivery issues, often seen with forwarded emails.
Impact on deliverability and sender reputation
When DMARC passes due to DKIM, the immediate impact on deliverability is generally minimal. Mailbox providers primarily rely on the DMARC pass/fail result to enforce policies (none, quarantine, or reject). If DMARC passes, even if SPF specifically failed, your emails are much less likely to be marked as spam or rejected outright.
However, it's not entirely without concerns. While a DMARC pass is the primary gatekeeper, some mailbox providers might still use SPF results as a secondary signal in their spam filtering algorithms. Consistently failing SPF, even with a DMARC pass, could subtly affect your overall sender reputation over time, potentially leading to increased spam folder placement, even if direct rejections are avoided. It's often seen as a "tidy thing" to fix, rather than a critical deliverability issue.
Furthermore, a lack of SPF authentication might make your domain slightly more susceptible to specific types of spoofing that target SPF weaknesses, although DMARC's overarching protection significantly mitigates this risk. It's always a best practice to have both SPF and DKIM passing and aligning if possible, as it provides stronger authentication signals and a more resilient email setup.
SPF failure (DKIM passes, DMARC passes)
Deliverability impact: Generally low, as DMARC passes due to DKIM. Emails should still reach the inbox, but may face minor scrutiny.
Reputation signals: May not be optimal. Some mail servers prefer both SPF and DKIM to pass cleanly.
Troubleshooting: Focus on identifying SPF misconfiguration or expected forwarding scenarios.
Both SPF and DKIM pass and align
Deliverability impact: Optimal deliverability. Strongest signals of legitimacy to all mailbox providers.
Reputation signals: Excellent. Builds maximum trust with receiving servers, enhancing domain reputation.
Troubleshooting: Less frequent, as authentication is robust. Focus on content and recipient engagement.
Best practices and troubleshooting
Even if DMARC passes with SPF failing, the goal should always be to achieve full SPF and DKIM alignment whenever possible. This proactive approach strengthens your email security posture and optimizes deliverability. Start by reviewing your DMARC reports, particularly the aggregate reports (RUA), which provide valuable insights into authentication results, including SPF failures, and their sources.
If you identify legitimate sending sources causing SPF failures, ensure their IPs are correctly included in your SPF record. For third-party senders, check if they offer custom SPF configuration or a dedicated subdomain for SPF. This is also a good opportunity to review your SPF record for any issues like too many DNS lookups, which can lead to SPF TempError results that prevent successful authentication.
For situations involving email forwarding, where SPF failure is often unavoidable, focus on ensuring your DKIM signature remains intact and aligns. Regularly monitoring your DMARC reports will help you catch any unexpected SPF failures or DMARC issues early, allowing for quick remediation. You can also review our guide on troubleshooting SPF and DMARC settings.
Not accounting for email forwarding, which commonly breaks SPF but not DKIM.
Assuming DMARC pass guarantees 100% inbox placement without considering all authentication signals.
Overlooking SPF record syntax errors or exceeding the 10-lookup limit.
Failing to update SPF records when adding new sending services, leading to legitimate SPF failures.
Expert tips
Implement DMARC with a `p=none` policy initially to gather data on SPF and DKIM authentication results without impacting delivery.
Utilize DMARC reporting tools to quickly pinpoint the root causes of any authentication issues.
Prioritize fixing SPF failures from your core sending infrastructure, as these are often most critical.
Remember that a DMARC pass means your email has met the minimum authentication requirements for policy enforcement, which is usually sufficient.
Consider that while DMARC handles policy, some mail servers use SPF and DKIM as independent signals for spam filtering.
Expert view
Expert from Email Geeks says DMARC's primary function is to check if either SPF or DKIM passes. If one does, the DMARC check will be successful. Both SPF and DKIM passing is the ideal scenario, but having one pass is sufficient for DMARC.
2022-11-08 - Email Geeks
Marketer view
Marketer from Email Geeks says it shouldn't affect deliverability if SPF fails but DKIM passes and DMARC passes. While there might be some unusual mail filters, generally, this setup is considered acceptable.
2022-11-08 - Email Geeks
Final thoughts
While a DMARC pass is a robust signal that your email is legitimate and helps ensure delivery, understanding the underlying SPF failure is still beneficial. In most cases where DKIM passes and aligns, the SPF failure will not critically impact deliverability. However, aiming for a fully authenticated email stream, with both SPF and DKIM passing and aligning, provides the strongest possible trust signals to mailbox providers. This comprehensive approach minimizes potential deliverability issues and strengthens your domain's overall reputation against spoofing and phishing.
