Why do email deliverability tools and Postmaster tools report conflicting authentication results?
Matthew Whittaker
Co-founder & CTO, Suped
Published 24 Jul 2025
Updated 19 Aug 2025
8 min read
It can be incredibly frustrating to see conflicting reports about your email authentication. One moment, your trusted email deliverability tool flags issues with SPF or DMARC, only for Google Postmaster Tools to report a perfect 100% success rate. This discrepancy leaves many of us wondering: which source is accurate, and what should be trusted?
Navigating these different data points is a common challenge for anyone serious about email deliverability. Understanding why these tools might present different views is the first step toward resolving the confusion and ensuring your messages consistently land in the inbox.
This guide will explore the reasons behind these conflicting authentication results and provide actionable steps to help you diagnose and resolve them effectively.
Email deliverability tools, often referred to as seed list or panel-based tools, operate by sending your emails to a predefined set of email addresses across various mailbox providers. They then analyze how these emails are handled, providing insights into inbox placement, spam folder delivery, and authentication status. These tools offer a broad, simulated view of your deliverability across a diverse recipient base.
On the other hand, Postmaster tools, like Google Postmaster Tools or Microsoft SNDS, provide direct data from the mailbox providers themselves. These tools offer a unique and authoritative perspective on how your emails are performing within that specific ecosystem. For instance, Google's Postmaster Tools dashboards display reputation and authentication data specifically for messages sent to Gmail accounts.
The fundamental difference lies in their data sources and methodologies. A seed list tool might be testing a limited set of permutations, while a Postmaster tool provides aggregated, real-world data from millions of mailboxes. This inherent difference is often the root cause of the conflicting authentication results you might observe.
Common causes of discrepancies
Conflicting authentication results often boil down to how SPF, DKIM, and DMARC are interpreted at different points in the email's journey, or issues with domain alignment. An email deliverability tool might report a failure due to an outdated seed list, a temporary network glitch on its side, or even a specific configuration that is less common but still valid.
Another common reason for these discrepancies is the specific domain being checked for authentication. For SPF, the RFC5321.MailFrom (envelope sender) domain is checked, while DMARC requires alignment between this domain and the RFC5322.From (header from) domain. If your email service provider uses a different envelope sender domain, a deliverability tool might report a non-aligned SPF pass, while Google Postmaster Tools, which sees the full picture, reports a DMARC pass because the underlying SPF or DKIM is passing for the domain that Gmail cares about. This is especially relevant if you're experiencing issues where Google Postmaster Tools shows a lower DMARC percentage than expected.
Another factor could be the volume of emails sent. Postmaster tools typically require a significant volume of mail to the respective mailbox provider before they display meaningful data. If you're testing with a very small send, your deliverability tool might have more immediate, albeit potentially less representative, feedback. For more insights into these complexities, check our article on common confusions in email authentication and DMARC reporting.
How to diagnose and troubleshoot conflicting results
When faced with conflicting reports, the most reliable source for debugging email authentication is the raw email header itself. Every email carries headers that detail its journey and the authentication results from the receiving server. This Authentication-Results header is the definitive record of how a specific mailbox provider (like Google, Yahoo, or Microsoft) evaluated your email's authentication.
To view this header, send a test email to a Gmail account you control, open the email, click the three dots next to the reply button, and select "Show original" or "View raw message." Look for the line that starts with Authentication-Results:. It will show the results for SPF, DKIM, and DMARC.
Example authentication results header
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of response@myhome.modernize.com designates 129.145.21.41 as permitted sender) smtp.mailfrom=response@myhome.modernize.com;
dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=modernize.com
This header is the definitive proof of how the receiving server evaluated your email. If it shows spf=pass, dkim=pass, and dmarc=pass from a major mailbox provider like Google, then your email authentication is indeed working correctly for that provider, regardless of what a third-party tool reports. This is particularly useful when Google Postmaster Tools is showing authentication failures despite SPF being configured.
Source of truth
For authentication results specifically with Gmail, always defer to Google Postmaster Tools. It's the most accurate source for how Google evaluates your email authentication.
Seed list tools
Methodology: Use a small, controlled set of mailboxes to simulate inbox placement.
Data scope: Provides an estimation across many ISPs, but may not reflect all real-world scenarios.
Accuracy: Useful for general trends, but can show false positives or negatives due to their limited scope.
Mailbox provider tools
Methodology: Collects aggregate data directly from live email traffic to their users.
Data scope: Offers authoritative insights for that specific mailbox provider only (e.g., Gmail for Google).
Accuracy: The definitive source for deliverability and authentication within their ecosystem.
Keep in mind that while Postmaster tools are excellent for the specific provider, they don't give you a holistic view of your deliverability across all mailbox providers. That's where a combination of tools and manual header analysis becomes essential.
Interpreting different authentication failures
Understanding the nuances of SPF, DKIM, and DMARC failures is key to interpreting conflicting reports. SPF (Sender Policy Framework) typically fails if the sending IP address is not authorized by the domain listed in the Return-Path header (also known as the MailFrom or envelope sender). If a third-party tool uses an outdated DNS cache or has a partial view of your SPF record, it might report a failure while the actual recipient server, with a full view, reports a pass. This scenario is common if your Google Postmaster Tools shows 0% SPF success.
DKIM (DomainKeys Identified Mail) failures indicate an issue with the cryptographic signature attached to your email. This could be due to the email content being modified in transit, an incorrect DKIM record in DNS, or an expired key. Deliverability tools might be more sensitive to minor changes or transient network issues that cause a DKIM check to fail, even if the primary mailbox providers can still validate it successfully.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) relies on both SPF and DKIM. A DMARC failure often means either SPF or DKIM (or both) failed, or, more commonly, that the authenticated domain did not align with the Header From domain. As the DMARC.org FAQ explains, DMARC allows domain owners to specify a policy for messages that do not pass authentication. If your DMARC authentication seems correct but you're still seeing failures, it's usually an alignment issue.
Moving forward with confidence
It's important to remember that Postmaster tools (e.g., Google Postmaster Tools) are providing a very specific, aggregated view from their perspective. They see all mail flowing into their network from your sending domains and IPs. Third-party tools, on the other hand, are making a best effort to replicate this, but they can't have the same comprehensive data. This is why when DMARC reports and Google Postmaster Tools conflict, the latter typically holds more weight for Gmail-specific deliverability.
The key is to use both types of tools strategically. Use Postmaster tools for an authoritative view of your performance with major mailbox providers, and use other deliverability tools for broader insights and to identify potential issues that might not be visible in Postmaster data due to volume or specific testing environments. Always cross-reference and investigate email headers if there's any doubt.
Views from the trenches
Best practices
Always check the raw email headers from a test email sent to a major mailbox provider like Gmail.
Prioritize the authentication results reported by Google Postmaster Tools for Gmail deliverability.
Ensure your SPF and DKIM domains align with your RFC5322.From header for DMARC pass.
Regularly monitor both deliverability tools and Postmaster tools, using each for its strengths.
Maintain consistent sending practices to build a strong domain and IP reputation.
Common pitfalls
Solely relying on a single deliverability tool's report without cross-referencing.
Ignoring the specific domains involved in SPF, DKIM, and DMARC checks.
Misinterpreting a temporary issue as a permanent configuration problem.
Not understanding the volume requirements for data to appear in Postmaster tools.
Overlooking the distinction between a softfail and a hardfail in SPF records.
Expert tips
When troubleshooting, simulate the exact sending method and recipient environment that is causing the reported discrepancies.
Consider that deliverability tools often use a different mail flow than your actual production emails, which can affect authentication.
A "pass" in your email headers from the target ISP is the ultimate confirmation of successful authentication for that specific message.
If your deliverability tool shows failures but Postmaster Tools shows passes, it's highly likely the issue is with the deliverability tool's methodology.
Use DMARC aggregate reports to get a comprehensive view of authentication outcomes across all receivers.
Marketer view
A deliverability tool indicated SPF and DMARC failures, while Google Postmaster Tools showed 100% authentication success.
2018-03-19 - Email Geeks
Marketer view
The issue might be localized to specific seed boxes rather than being a universal failure.
Google Postmaster Tools or 
Microsoft SNDS, provide direct data from the mailbox providers themselves. These tools offer a unique and authoritative perspective on how your emails are performing within that specific ecosystem. For instance, Google's Postmaster Tools dashboards display reputation and authentication data specifically for messages sent to Gmail accounts.
Gmail account you control, open the email, click the three dots next to the reply button, and select "Show original" or "View raw message." Look for the line that starts with Authentication-Results:. It will show the results for SPF, DKIM, and DMARC.
