How accurate is SNDS and Google Postmaster Tools reputation data?
Michael Ko
Co-founder & CEO, Suped
Published 30 Jul 2025
Updated 16 Aug 2025
7 min read
Email deliverability heavily relies on sender reputation. For anyone sending emails, understanding how mailbox providers perceive your sending practices is crucial. Two primary tools that offer insights into this perception are Google Postmaster Tools (GPT) and Microsoft Smart Network Data Services (SNDS). They offer a window into how Gmail and Outlook.com view your email sending practices.
While these tools are invaluable for troubleshooting and maintaining good sender reputation, it's important to understand their accuracy and limitations. I've often seen discussions among deliverability professionals about how to interpret the data from GPT and SNDS, especially when it doesn't align with observed inbox placement.
Understanding Google Postmaster Tools’ insights
Google Postmaster Tools provides crucial dashboards that offer insights into your sending performance, including Spam Rate, IP Reputation, Domain Reputation, Feedback Loop, and Authentication. These metrics are essential for diagnosing and resolving email deliverability issues. Iterable provides a deep dive into these very dashboards, explaining how they can be leveraged.
However, the data in Google Postmaster Tools can sometimes be delayed or show inconsistencies, particularly with low sending volumes. For example, some senders have reported that domain reputation data may not update promptly. This means a real-time issue might not immediately appear in your reports, requiring you to look at trends over longer periods rather than day-to-day fluctuations.
A critical aspect to understand is that Gmail's reputation can act as a trailing indicator. While improvements in your sending practices may take days or even weeks to be reflected in your GPT data, a rapid decline can appear very quickly. This highlights the importance of consistent best practices and regular monitoring.
The reliability of Microsoft SNDS data
Microsoft Smart Network Data Services (SNDS) primarily focuses on IP reputation, providing an indication of how Microsoft's email services view your sending IP addresses. It also provides some data on spam rates and authentication. You can freely check your sender reputation with both Google Postmaster Tools and Microsoft SNDS.
However, a common sentiment among deliverability professionals is that SNDS data, particularly its color-coded reputation indicators, can be misleading. I've heard many instances where SNDS reports all IPs as green even when email campaigns are experiencing significant deliverability issues to Microsoft inboxes. This suggests that the SNDScolors may not always accurately reflect the true situation.
This perceived inaccuracy stems from the suspicion that SNDS operates on a reputation system that hasn't been updated in line with Microsoft's actual spam filters. It's often described as a separate system that doesn't directly govern inbox placement at Microsoft mailboxes. Therefore, while SNDS can offer some indication, it should be viewed as a supplementary tool rather than a definitive source for Microsoft deliverability.
The perceived inaccuracies in both GPT and SNDS stem from a combination of factors, including the proprietary nature of ISP filtering algorithms, data aggregation delays, and the specific metrics each tool chooses to expose. Neither tool offers a comprehensive, real-time snapshot of your entire deliverability landscape. We often encounter questions about how to interpret discrepancies between these tools and other reporting systems.
For example, a strong IP reputation in Google Postmaster Toolsdoes not automatically guarantee excellent inbox placement if other factors like content quality, recipient engagement, or a high spam complaint rate are neglected. The overall sender reputation is a complex interplay of many signals beyond what these tools can capture.
It's crucial to remember that Google Postmaster Tools and SNDS are designed to give high-level insights into your aggregate sending behavior, not to debug every individual email. Relying solely on them without cross-referencing with bounce rates, spam complaints from your Email Service Provider (ESP), and engagement metrics can lead to misinterpretations. For example, the spam rate in GPT might be higher than your ESP reported spam rate.
To get a truly accurate picture, I recommend a multi-faceted approach. You need to combine the data from these tools with your internal sending metrics. This integrated view allows you to accurately test and measure email deliverability.
Maximizing insights from reputation data
Despite their known limitations, Google Postmaster Tools and Microsoft SNDS remain indispensable resources for anyone sending to Gmail and Outlook.com inboxes. The key is to understand what they tell you and, more importantly, what they don't.
For instance, if GPT consistently shows a bad or low reputation for your domain or IP, it's a strong indicator of serious underlying issues that demand immediate attention. Similarly, if SNDS indicates your IP is on a blacklist (or blocklist), that's actionable intelligence you need to respond to, regardless of its general color status. You can use a blocklist checker for this.
I suggest using these tools as directional indicators rather than absolute truths. Focus on long-term trends instead of daily fluctuations, as a sudden shift, even if not immediately explained, warrants deeper investigation. It is useful to combine insights from these tools with a blocklist monitoring strategy.
To truly improve your email deliverability and sender reputation, you need a holistic approach. This includes meticulous list hygiene, engaging content, and robust email authentication protocols such as SPF, DKIM, and DMARC. Implementing a DMARC monitoring solution is highly recommended.
A holistic view of email reputation
The accuracy of SNDS and Google Postmaster Tools reputation data is not absolute. While they offer invaluable, direct feedback from two of the largest mailbox providers, their data can be delayed, inconsistent, or only reflect a subset of an ISP's internal reputation system.
I've found that these tools are most effective when used as part of a comprehensive deliverability monitoring strategy. They provide critical warning signs and broad performance trends that might not be visible elsewhere. Understanding the data requirements and freshness for each is key.
Combining the insights from Google Postmaster Tools and SNDS with your own sending data, such as bounce rates and explicit spam complaints, offers a more complete and actionable picture of your email program's health.
Views from the trenches
Best practices
Actively monitor trends over time in both tools, rather than focusing on daily fluctuations.
Always cross-reference the data from GPT and SNDS with your own ESP's reporting, especially for bounce rates and spam complaints.
Implement strong email authentication protocols (SPF, DKIM, DMARC) as these are fundamental to building and maintaining good sender reputation.
Maintain excellent list hygiene to avoid spam traps and reduce complaint rates, which directly impact reputation.
Use other deliverability metrics like open rates, click-through rates, and unsubscribes to get a more complete picture of recipient engagement.
Common pitfalls
Solely relying on SNDS's green color status as an indicator of good deliverability to Microsoft inboxes.
Expecting real-time updates from Google Postmaster Tools, especially during periods of low sending volume or when reputation is improving.
Ignoring slow degradation of reputation in GPT because it still shows as 'high', rather than investigating subtle shifts.
Assuming a good reputation in these tools means your emails will bypass all spam filters, overlooking content quality and engagement.
Not understanding that these tools are postmaster-specific views, not comprehensive deliverability audits across all ISPs.
Expert tips
SNDS uses a reputation system that may not align directly with Microsoft's real-time inbox placement filters.
Google reputation data often trails, taking time to reflect improvements but reacting quickly to negative events.
Even when reputation appears high in GPT, a slow decline in deliverability can indicate underlying issues not immediately visible.
The historical context of these tools suggests that their data may not always reflect the most current filtering logic.
Continuous monitoring and adaptation based on combined data sources are more effective than relying on a single tool.
Expert view
Expert from Email Geeks says: SNDS seems to be showing all IPs green for yesterday, as seen by multiple ESPs, indicating the colors might not always reflect the true situation.
December 10, 2021 - Email Geeks
Marketer view
Marketer from Email Geeks says: The colors in SNDS are consistently misleading, and it's a common observation among deliverability professionals.
Google Postmaster Tools (GPT) and 
Microsoft Smart Network Data Services (SNDS). They offer a window into how 
Gmail and 
Outlook.com view your email sending practices.
