Why were Microsoft FBL reports not being received in September 2020?
Michael Ko
Co-founder & CEO, Suped
Published 26 Apr 2025
Updated 18 Aug 2025
6 min read
In September 2020, many email service providers (ESPs) and large senders experienced a peculiar issue: a sudden halt in the reception of Feedback Loop (FBL) reports from Microsoft. This disruption in data flow caused significant concern across the email community, as FBLs are a critical component of maintaining healthy sender reputation and ensuring optimal deliverability.
For several days, data from the Microsoft Junk Mail Reporting Program (JMRP) was either delayed or completely missing, leaving senders without crucial insights into how their emails were being perceived by recipients. This article will delve into the likely reasons behind this outage and explore the broader implications for email deliverability professionals.
The role of FBLs in email deliverability
Feedback Loops (FBLs), also known as complaint feedback loops, are a cornerstone of responsible email sending. They provide a mechanism for internet service providers (ISPs) to inform senders when a recipient marks their email as spam or junk. This essential feedback allows senders to identify problematic campaigns, remove disengaged users from their lists, and ultimately improve their sender reputation.
Without timely FBL data, senders operate in the dark regarding their spam complaint rates. High complaint rates are a strong indicator of low sender quality and can lead to severe consequences, including IP address and domain blocklisting (or blacklisting). Providers like Microsoft rely heavily on these signals to filter incoming mail, so a disruption in the FBL system means senders lose a vital early warning system.
Monitoring FBLs is a proactive measure to prevent deliverability issues. It helps in maintaining a clean subscriber list, ensuring that emails reach the inbox, and avoiding costly blocklist (or blacklist) entries. When FBLs stop flowing, even a well-managed sending program can face unforeseen challenges.
The September 2020 disruption timeline
Reports from various email professionals indicated that the outage began around September 13th and extended through September 22nd, 2020. During this period, numerous senders confirmed they were not receiving their expected JMRP FBL reports, causing widespread concern about potential hidden deliverability problems.
Date (approx.)
Event
Observed Impact
September 13-17, 2020
Individual senders begin noticing a drop in, or complete cessation of, Microsoft FBL reports.
Early signs of inconsistent or missing data for specific date ranges, raising initial alarms among deliverability teams.
September 17-18, 2020
Widespread confirmation among ESPs and large senders that Microsoft FBL data had ceased.
Major blind spot for complaint rates, inability to react to abuse, and uncertainty about ongoing sender reputation.
September 22, 2020
Microsoft FBL reports resume, often backdated to include the missing period.
Data integrity largely restored, allowing senders to catch up on delayed insights and resume normal monitoring.
While Microsoft did not release a specific statement directly addressing FBL report disruptions, multiple reports from that period indicate that Microsoft experienced security log data loss during September 2020 due to a bug. This issue, which impacted their internal logging systems, could very well have affected the generation and transmission of FBL data, as these reports are essentially aggregated logs of user complaints. A partial loss of security log data for several weeks during that month could easily explain the FBL outage.
The fact that the reports eventually returned and were backdated suggests that Microsoft's systems either caught up with the processing once the underlying issue was resolved, or that the data was being logged but not transmitted. This event served as a stark reminder of the complexities involved in managing large-scale email ecosystems and the potential for unforeseen outages to impact critical feedback mechanisms.
Mitigating the impact of FBL outages
When FBL reports stop flowing, the immediate challenge for senders is the loss of visibility into complaint rates. This blind spot can lead to higher spam rates and an increased risk of IP or domain blocklisting (or blacklisting) if problematic sending patterns go unnoticed. While a temporary outage might not cause immediate catastrophic damage, prolonged disruptions can severely impact sender reputation and email deliverability.
Normal FBL operation
Timely feedback on spam complaints via FBL reports.
Proactive removal of complaining users, improving list hygiene.
Clear visibility into user engagement and potential abuse patterns.
Reduced risk of IP or domain blocklisting (blacklist) due to high complaints.
During FBL outage
Lack of immediate feedback on spam complaints, creating a blind spot.
No direct mechanism to remove complaining users, potentially impacting sender reputation.
To mitigate the impact of such outages, senders should rely on other available metrics and best practices. Continue to monitor engagement rates, open rates, and click-through rates as alternative indicators of recipient interest. Pay close attention to bounces and suppressions. While not a direct substitute for FBLs, these metrics can provide some insight into email performance.
It is also crucial to maintain excellent list hygiene proactively. Regularly clean your lists of inactive subscribers, suppress hard bounces, and ensure all opt-in processes are clear and consented. These foundational practices help reduce the likelihood of complaints even when FBL data is unavailable.
Lessons learned and future preparedness
The September 2020 FBL outage underscored the importance of not relying on a single data source for deliverability monitoring. While FBLs are invaluable, a robust deliverability strategy requires a multi-faceted approach. This includes tracking sender reputation metrics across various platforms, even if they aren't FBLs themselves.
Key takeaways for FBL monitoring
Diversify monitoring: Don't depend solely on FBL reports. Use a combination of tools and metrics to gauge performance. For example, Microsoft SNDS data is another key resource.
Proactive list hygiene: Regularly clean and validate your email lists to minimize complaints, regardless of FBL status. Removing unengaged subscribers is key.
Track engagement: Monitor open rates, click-through rates, and conversion metrics as supplemental indicators of list health. Consistent email deliverability tests can provide immediate feedback.
Ultimately, the incident served as a powerful reminder that email deliverability is a dynamic and complex field. While outages like this are rare, being prepared with diversified monitoring strategies and maintaining fundamental email best practices are paramount for ensuring consistent inbox placement, even when critical feedback mechanisms face temporary disruptions. Understanding how FBL reports work with IP addresses can also help troubleshoot issues.
Views from the trenches
Best practices
Regularly audit your subscriber acquisition methods to ensure only consented users are added to your lists.
Segment your audience and tailor content to their interests to reduce the likelihood of spam complaints.
Implement a clear and easy-to-find unsubscribe mechanism in every email, as a preference over spam complaints.
Beyond FBLs, utilize all available postmaster tools, like
Common pitfalls
Over-relying on a single FBL provider without cross-referencing data from other sources.
Ignoring subtle shifts in engagement metrics when FBL data becomes unavailable, missing early warning signs.
Not having an alternative plan for identifying problematic campaigns during FBL outages, leading to prolonged issues.
Neglecting to clean inactive subscribers, which can inflate complaint rates once FBLs resume.
Expert tips
During an FBL outage, focus on positive engagement signals, such as opens and clicks, while awaiting data restoration.
Communicate proactively with your email service provider (ESP) or internal teams about any observed data discrepancies.
Leverage DMARC reports to identify potential abuse or deliverability issues, even if FBLs are temporarily down.
Automate list cleaning processes to quickly remove hard bounces and subscribers who repeatedly ignore your emails.
Expert view
Expert from Email Geeks says they confirmed the issue, with the last report received on midnight of the 18th.
September 21, 2020 - Email Geeks
Marketer view
Marketer from Email Geeks says their reports also stopped around the beginning of the 18th.
September 21, 2020 - Email Geeks
Ensuring continuous email insight
The Microsoft FBL report disruption in September 2020 was a significant event for email senders, highlighting the fragile nature of relying on a single data stream for critical deliverability insights. It underscored the need for resilient monitoring strategies that can adapt to unforeseen outages from major email providers. Building a comprehensive approach to email deliverability ensures that even when one data source is temporarily unavailable, you still have other indicators to guide your sending decisions and maintain sender reputation.
By understanding the role of FBLs, staying informed about industry-wide issues, and implementing robust internal monitoring, email professionals can navigate such challenges effectively. While the exact cause for the September 2020 outage was not explicitly confirmed by Microsoft, the widely reported security log issues provide a strong potential explanation for the disruption to complaint data flow. This experience reinforces the idea that constant vigilance and adaptability are key to successful email delivery.
Microsoft. This disruption in data flow caused significant concern across the email community, as FBLs are a critical component of maintaining healthy sender reputation and ensuring optimal deliverability.
