What is the new or undocumented data available in the Google Postmaster Tools API?
Matthew Whittaker
Co-founder & CTO, Suped
Published 7 Jun 2025
Updated 19 Aug 2025
7 min read
Google Postmaster Tools offers valuable insights for email senders, helping us understand our email performance and how our messages are delivered to Gmail users. It's a critical resource for maintaining good email deliverability.
While the web interface has seen updates, particularly with the transition to V2 dashboards, the underlying API often reveals data points that are either newly introduced or not yet fully documented. This can present both opportunities and challenges for senders who rely on automated data retrieval.
I've recently noticed some interesting, undocumented metrics showing up when interacting with the Google Postmaster Tools API. This kind of data, even if not officially released with full explanations, can hint at what Google is tracking and prioritizing, offering an early look into potential future features or enhanced insights.
One specific metric, userReportedSpamRatioUpperBound, caught my attention, as it appeared in API responses but yielded null values for all monitored domains. This suggests either a phased rollout, a bug, or an internal metric not yet ready for public consumption, similar to past situations with Outlook.com SNDS. This kind of discovery prompts a deeper dive into what else might be lurking in the API responses.
Understanding the GPT API landscape
The official Google Postmaster Tools API is designed to allow bulk email senders to programmatically gather metrics and integrate this data into their own systems. This programmatic access is crucial for large-scale operations and detailed analysis.
However, there's often a discrepancy between the data visible in the web interface and what's available through the API. The web interface tends to be updated more frequently with new dashboards and features, while the API, specifically the V1 endpoints, can lag behind. This creates a situation where valuable information might be present in one place but not the other, leading to a fragmented view for senders.
The ongoing discussion about a potential V2 API for Google Postmaster Tools highlights this gap. Senders have noted that the web interface has already upgraded to V2, offering new metrics and improved accuracy, yet the API remains limited to its V1 endpoints. This makes it challenging to access the latest insights programmatically.
The mystery of 'userReportedSpamRatioUpperBound'
During recent API interactions, the field userReportedSpamRatioUpperBound appeared in the data structure, even though it's not explicitly documented in the official Gmail API reference for TrafficStats. The value, however, consistently returned as null across numerous domains. This could imply a metric currently in development, a specific internal test, or data related to a pilot program that is not broadly available yet.
Uncovering the undocumented data
Beyond the specific userReportedSpamRatioUpperBound field, monitoring API responses closely can reveal other subtle changes or new fields that might not be announced publicly. These could relate to new compliance metrics, expanded spam classifications, or even more granular data points on user engagement.
For instance, discussions among deliverability professionals have hinted at data points previously available only in specific pilot programs, such as those related to political email initiatives. It's possible that Google is slowly integrating these into the broader API or web interface, even if not fully documented. Keep an eye on the Postmaster Tools dashboards for changes. If you encounter missing data, it might be tied to these ongoing rollouts, as discussed in our article on why Google Postmaster data is missing.
Unearthing this undocumented data requires consistent monitoring of API responses and a keen eye for new fields or changes in existing data structures. Sometimes, even if a value is null, its presence in the schema indicates Google's interest in tracking that specific metric. This proactive approach can give you an edge in understanding deliverability trends before they become widely known.
Documented API metrics
Spam rate: Percentage of emails marked as spam by users and Gmail's spam filter.
IP reputation: How likely emails from this IP are to go to spam.
Domain reputation: How likely emails from this domain are to go to spam.
Feedback loop (FBL): Data on emails marked as spam by Gmail users.
Undocumented/new API metrics
User-reported spam upper bound: Possible new metric indicating maximum user spam complaints.
Compliance status: Likely related to Google's new sender requirements.
Engagement insights: Speculative, could include read rates or reply rates.
Implications for deliverability
Any new metric, documented or not, from Google's Postmaster Tools can have significant implications for email deliverability. Google is a major inbox provider, and their signals are critical. Even a seemingly minor field like userReportedSpamRatioUpperBound could eventually become a key indicator for how your emails are perceived by Gmail.
Senders should be proactive in adapting their strategies. If Google is tracking new compliance metrics, for example, it means their enforcement of sender guidelines might become even more stringent. Understanding these subtle shifts is vital for maintaining a healthy sender reputation and avoiding blocklists (or blacklists).
This evolution in metrics underscores the importance of continuous monitoring of your email performance. Relying solely on the public dashboards might mean missing early warnings or opportunities to fine-tune your sending practices. It's another layer to consider in the complex landscape of email deliverability, especially if you want to avoid emails going to spam.
Example API request (simplified)HTTP
GET https://gmailpostmastertools.googleapis.com/v1/domains/{domainId}/trafficStats
Authorization: Bearer YOUR_ACCESS_TOKEN
Navigating the API challenges
Navigating the Google Postmaster Tools API, especially with undocumented features, presents its own set of challenges. The lack of official documentation means that integrating these insights into automated systems can be complex and prone to unexpected changes. Developers need to be vigilant about API responses and schema changes.
To access any potentially new or undocumented data, it's crucial to ensure your API client libraries are up to date. This ensures you're interacting with the latest version of the API and can potentially see new fields that are being rolled out. Google often deploys features progressively, so not all users might see new data at the same time.
The situation with undocumented API fields is a reminder that while Postmaster Tools is incredibly useful, it's part of an evolving ecosystem. Staying informed through community discussions and careful observation of API behavior is key. It helps you stay ahead of potential issues and leverage every available data point to improve your sender performance and email deliverability.
Views from the trenches
Best practices
Monitor API response schemas diligently for any new or modified fields, even if initially null.
Keep your Google API client libraries updated to ensure access to the latest data and features.
Participate in email deliverability community forums to share findings and learn from others' experiences.
Correlate changes in undocumented API metrics with your own deliverability trends.
Common pitfalls
Relying solely on the Google Postmaster Tools web interface for all data insights, missing API-specific nuances.
Ignoring API fields that return null values, as they might indicate future important metrics.
Using outdated API client libraries, which can prevent access to new or hidden data.
Neglecting to monitor API rate limits when programmatically accessing Postmaster Tools data.
Expert tips
Anticipate Google's future sender requirements by observing emerging metrics, even if undocumented.
Prepare for potential shifts in compliance expectations by understanding what data Google might be collecting.
Utilize internal discussions and feedback from Postmaster Tools to refine your email sending practices.
Consider how these API changes might impact your DMARC monitoring and overall email security posture.
Expert view
Expert from Email Geeks says that regarding the userReportedSpamRatioUpperBound being null, this could be an indicator of an internal metric that Google is testing before rolling it out. It's not uncommon for them to gradually release new data points.
2023-09-14 - Email Geeks
Marketer view
Marketer from Email Geeks says that the discrepancies between the Postmaster Tools web interface and the API can be frustrating, meaning we often have to check both to get a complete picture, which adds manual work.
2023-09-14 - Email Geeks
Final thoughts on evolving API insights
The existence of new or undocumented data points within the Google Postmaster Tools API serves as a vital reminder for email senders to remain adaptive and diligent. While official documentation provides a foundational understanding, a deeper, proactive investigation into API responses can unveil early indicators of Google's evolving deliverability metrics and priorities.
These subtle shifts, whether a temporary bug or a phased rollout, directly impact how your emails land in Gmail inboxes. By actively monitoring the API, keeping client libraries updated, and engaging with the broader deliverability community, you can better prepare for changes, optimize your sending practices, and ensure your messages consistently reach their intended recipients. It’s about leveraging every available signal to maintain strong email deliverability.
Google Postmaster Tools API. This kind of data, even if not officially released with full explanations, can hint at what Google is tracking and prioritizing, offering an early look into potential future features or enhanced insights.
Outlook.com SNDS. This kind of discovery prompts a deeper dive into what else might be lurking in the API responses.
Google is slowly integrating these into the broader API or web interface, even if not fully documented. Keep an eye on the Postmaster Tools dashboards for changes. If you encounter missing data, it might be tied to these ongoing rollouts, as discussed in our article on why Google Postmaster data is missing.
