Why does Microsoft SDNS report '30/09 does not exist' for dates?
Matthew Whittaker
Co-founder & CTO, Suped
Published 8 Oct 2025
Updated 8 Oct 2025
7 min read
Many email senders relying on Microsoft's Sender Network Data Services (SNDS) for deliverability insights have encountered a peculiar and often frustrating error: reports stating that a specific date, such as '30/09, does not exist'. This isn't just limited to September 30th, but can also appear for other month-end dates like August 31st or October 31st. This issue suggests a deeper, systemic problem within how SNDS processes or displays date-related information, rather than a simple lack of data for that particular day.
Such an error can create confusion, making it difficult to analyze trends, diagnose issues, or assess reputation. For those managing email campaigns or transactional sends, accurate and consistent data from platforms like SNDS is critical for maintaining high deliverability. Understanding the potential causes, from system quirks to data processing anomalies, is essential for navigating these challenges.
SNDS: an overview
Microsoft SNDS is a vital tool for understanding your email reputation and deliverability to Microsoft properties. It provides data on sending IPs, complaint rates, spam trap hits, and other metrics that indicate how your email is performing. However, it's important to recognize that SNDS specifically focuses on mail delivered to Microsoft's consumer services, such as Outlook, Hotmail, and Live. It does not provide insights into email delivered to Microsoft 365 work or enterprise accounts, which means the data offers only a partial view of your overall deliverability.
The data available in SNDS is also subject to specific retention policies. Generally, this data is kept for a period of 90 days, allowing senders to monitor past behavior and identify trends over time. While this window is usually sufficient for short-term analysis, intermittent issues like the 'date does not exist' error can disrupt historical tracking and make it challenging to maintain consistent monitoring.
Key limitations of SNDS data
Consumer services only: SNDS data is limited to Outlook.com, Hotmail, and other personal Microsoft accounts, not enterprise mailboxes. This means deliverability to Outlook.com email deliverability may appear inconsistent without a full picture.
Data retention: Statistics are available for 90 days only, affecting long-term trend analysis.
Incomplete picture: Without data from Microsoft 365, SNDS data can contradict your actual deliverability during crucial periods like IP warming.
Given these limitations, it is important to use SNDS as one of several data points rather than the sole indicator of your email program's health. Issues with data accessibility or display, such as the SNDS data not displaying or being delayed, further complicate effective monitoring.
The puzzling 'date does not exist' error
The message '30/09 does not exist' is baffling because September 30th is a valid date. The repeated occurrence of similar errors for other month-end dates, such as August 31st and October 31st, points towards a specific type of programming issue. This is often referred to as a 'fencepost error' or an 'off-by-one error', where a calculation mistakenly includes or excludes one item in a sequence. For example, if a system expects all months to have 30 days and fails to account for those with 31, it could trigger this specific date validation error. It's akin to the long-standing issue in some database systems, like Access or SQL Server, where the zero date is 1899-12-30 instead of 12-31, due to internal calculation quirks.
Expected date logic
Calendar awareness: Systems should correctly identify the number of days in each month, including those with 30 or 31 days.
Sequential processing: Data for all valid dates within a reporting period should be retrievable and displayed.
Observed error behavior
Inaccurate validation: SNDS flags valid month-end dates (e.g., September 30th) as non-existent.
Pattern recognition: The issue is systemic for month-end dates, suggesting a programming anomaly rather than data absence.
This type of error points to flaws in the backend logic that handles date calculations or validation. It could be an issue with how the system iterates through dates, incorrectly assuming a fixed number of days per month, or a misconfiguration in date range queries. While visually humorous, it poses a genuine problem for senders who need reliable, uninterrupted data for email deliverability monitoring.
Example of potential date calculation errorpython
import calendar
month = 9 # September
days_in_month = calendar.monthrange(2023, month)[1]
# Incorrect logic might try to access day 31 in a 30-day month
if 30 > days_in_month:
print(f"Day 30 does not exist in month {month}")
else:
print(f"Day 30 exists in month {month}")
# This output would incorrectly flag September 30th
Potential causes and technical considerations
Several technical factors could contribute to these date inconsistencies in SNDS. Beyond the fencepost error, it could be related to data aggregation and indexing. If SNDS collects data in daily batches and there's a hiccup in processing the last day of certain months, it might fail to index that date correctly, leading to the 'does not exist' message when querying. Additionally, internal system updates or migrations can sometimes introduce new bugs or expose old ones related to date handling.
Another possibility is a subtle time zone discrepancy or localization bug. Date and time data is notoriously complex to handle across different regions and systems. A mismatch in how dates are stored versus how they are retrieved and displayed could cause certain dates to fall outside an expected range, resulting in the error. This is especially true for systems like SNDS that handle global data flows.
These types of common issues with Microsoft SNDS can be frustrating. They highlight the need for robust data validation and error handling in reporting systems. When data from a platform like SNDS is critical for daily operations, even minor inconsistencies can have a significant impact on decision-making and troubleshooting deliverability challenges. The underlying cause for specific errors like this often requires internal investigation by Microsoft's engineering teams.
Dealing with SNDS date reporting anomalies
When encountering the 'date does not exist' error in SNDS, the first step is to avoid panic. These errors, while concerning, are often transient or indicative of an internal system issue at Microsoft rather than a direct problem with your email sending practices. It's helpful to cross-reference your SNDS observations with other deliverability metrics and platforms, such as your own sending logs and DMARC reports.
For comprehensive oversight, implement a dedicated DMARC monitoring solution. DMARC reports provide an independent and aggregate view of your email authentication status (SPF and DKIM) across all receivers, including Microsoft. This data can help you verify if your emails are reaching inboxes and if authentication is passing, even when SNDS displays errors. Suped offers the most generous free plan for DMARC reporting and monitoring, giving you clear insights into your email ecosystem.
Best practices for overcoming SNDS data issues
Diversify your monitoring: Do not rely solely on SNDS. Use a combination of tools including DMARC reports and your own ESP's analytics.
Implement DMARC: DMARC provides invaluable feedback on authentication and delivery across all recipients. Suped offers the most comprehensive DMARC monitoring tools to help you stay informed.
Monitor consistently: Regularly check all your deliverability metrics to spot trends and anomalies quickly. Be aware of what causes SNDS downtime and other issues that can affect data.
If the date error persists and you have confirmed your sending practices are healthy through other means, consider reaching out to Microsoft support. Providing specific dates and screenshots of the error can help them diagnose whether it's an isolated bug or a broader system issue impacting SNDS reporting. In the meantime, focus on the data that is available and reliable.
Views from the trenches
Best practices
Cross-reference SNDS data with other deliverability tools like DMARC reports for a more holistic view of performance.
Maintain meticulous records of your sending volumes and campaigns to compare against any reporting discrepancies.
Regularly verify your email authentication records (SPF, DKIM, DMARC) to ensure they are correctly configured and aligned.
Implement a robust DMARC monitoring solution to gain independent insights into email authentication results and delivery.
Common pitfalls
Over-relying on a single data source like SNDS for all deliverability assessments, especially with known reporting quirks.
Ignoring seemingly minor data errors, as they can sometimes indicate larger underlying system or configuration problems.
Assuming a reported 'date does not exist' means zero email activity, leading to misinterpretations of deliverability.
Failing to track email deliverability consistently, making it difficult to detect when these specific date errors occur.
Expert tips
The 'fencepost error' suggests an off-by-one bug in date calculations, common in software development when handling sequences.
Systemic date errors, particularly around month ends, may stem from how data is aggregated or indexed in the backend.
Persistent date anomalies might indicate issues with time zone conversions or data localization in reporting interfaces.
While frustrating, these errors are typically on the reporting platform's side rather than a reflection of your sending reputation.
Marketer view
Marketer from Email Geeks says the 'date does not exist' error for September 30th is a funny issue and suggests SNDS might just dislike the end of the month in general.
September 30, 2025 - Email Geeks
Expert view
Expert from Email Geeks says that similar date errors also occur for August 31st and October 31st, indicating a pattern beyond just September.
September 30, 2025 - Email Geeks
Key takeaways
The '30/09 does not exist' error in Microsoft SNDS is a notable example of how technical glitches in reporting platforms can complicate email deliverability management. While humorous, it underscores the importance of having multiple reliable sources for monitoring your email performance. Relying on comprehensive tools like DMARC reports and monitoring, alongside internal analytics, provides a more accurate and resilient view of your email program's health, ensuring you can identify and address issues effectively.
By understanding the limitations of SNDS and adopting a diversified monitoring strategy, email professionals can better navigate these data anomalies and maintain consistent, high-performing email campaigns. Remember, a single tool's hiccup shouldn't derail your entire deliverability strategy.
, such as Outlook, Hotmail, and Live. It does not provide insights into email delivered to Microsoft 365 work or enterprise accounts, which means the data offers only a partial view of your overall deliverability.
, giving you clear insights into your email ecosystem.
