Summary
A sudden surge in Microsoft's Feedback Loop (FBL) complaint rates, as reported through Mailgun, typically signals a significant shift in how recipients perceive your emails. While it could, in some cases, stem from Mailgun beginning to forward previously unreceived complaint data, the overwhelming consensus points to issues within the sender's own email program, such as declining list quality or problematic sending practices. These complaints, processed by Mailgun from Microsoft's Junk Mail Reporting Program (JMRP/JMRPP), directly impact sender reputation with Outlook.com and Exchange Online, indicating recipients are actively marking messages as spam. Common culprits include sending to old or unengaged lists, acquiring lists without explicit consent, sending irrelevant or unexpected content, or a sudden increase in sending volume that overwhelms recipients. Ultimately, a high FBL rate is a direct measure of recipient dissatisfaction and underscores the critical need for robust list hygiene, content relevance, and adherence to email deliverability best practices.
Key findings
- Reporting Changes: A sudden appearance of Microsoft FBL complaints via Mailgun might indicate Mailgun has recently started forwarding previously unseen complaint data to your webhooks, rather than the JMRPP program itself being new.
- List Quality Decline: The primary cause for a sudden increase in FBL complaints is often a decline in list quality or a recent change in sending practices, such as sending to old, unengaged, or unverified email addresses.
- Sender Reputation Impact: High FBL complaint rates, especially with Microsoft's JMRP, are a direct and immediate indicator of poor sender reputation, which leads to stricter filtering by Microsoft's systems.
- Recipient Dissatisfaction: A surge in complaints signifies that recipients are actively marking your messages as junk or spam due to irrelevance, unexpected content, lack of engagement, or unsolicited emails.
- Customer Sending Behavior: The increase in complaint rates is frequently linked to specific customer sending behavior, such as reactivating old lists, acquiring new lists with low engagement, or significant changes in email content or sending volume.
- Shared IP Risk: If using Mailgun's shared IP addresses, a sudden surge in FBL complaints could potentially be attributed to the poor sending practices of other users on the same IP pool, impacting your deliverability.
Key considerations
- Clean Email Lists: Regularly clean email lists by removing inactive, unengaged, or unverified subscribers to maintain list quality.
- Validate Consent: Ensure all subscribers have given explicit consent to receive your emails, avoiding purchased or old, unengaged lists.
- Segment & Ramp Up: Segment your audience and gradually increase sending volume to new or less engaged segments, rather than sending large blasts.
- Review Content & Frequency: Assess your email content for relevance and align it with subscriber expectations. Evaluate sending frequency to avoid overwhelming recipients.
- Monitor Specific Campaigns: Identify and analyze specific campaigns or audience segments that may be contributing to the sudden increase in complaints.
- Provide Unsubscribe Options: Always include clear and easy-to-find unsubscribe options in your emails.
What email marketers say
12 marketer opinions
A sudden rise in Microsoft's Feedback Loop (FBL) complaint rates, reported through Mailgun, generally indicates that recipients are actively marking your emails as spam. While there's a theory that Mailgun might have recently started forwarding these complaints more diligently, thereby revealing previously unseen data, the overwhelming consensus points to fundamental issues within the sender's own email program. These complaints, which are processed via Mailgun from Microsoft's Junk Mail Reporting Program (JMRP), directly reflect recipient dissatisfaction. Common reasons for such a surge include poor list hygiene, sending to unengaged or unverified subscribers, a lack of explicit consent, or delivering irrelevant or unexpected content. This spike underscores the urgent need to re-evaluate your list quality, content strategy, and adherence to email deliverability best practices, as it directly impacts your sender reputation and deliverability to Microsoft inboxes.
Key opinions
- Potential Reporting Change: One theory suggests Mailgun may have recently begun forwarding Microsoft's JMRP complaints to webhooks, making previously unseen data suddenly visible.
- Direct Recipient Feedback: A higher FBL complaint rate directly signifies that recipients are actively marking your emails as spam, indicating dissatisfaction with your messages.
- List Quality Issues: The primary cause is often a decline in list quality, such as sending to unengaged, old, or unverified email addresses, or to lists acquired without explicit consent.
- Content or Volume Mismatch: Irrelevant or unexpected content, coupled with a sudden increase in sending volume, can trigger negative reactions and lead recipients to report spam.
- Impact on Sender Reputation: High FBL complaint rates, especially with Microsoft, directly harm your sender reputation, leading to increased filtering and deliverability challenges.
- Shared IP Influence: If using Mailgun's shared IP addresses, the poor sending practices of other users on the same IP pool could inadvertently affect your FBL rates and deliverability.
- Specific Campaign Link: The increase in complaints is frequently tied to a specific campaign, segment, or the reactivation of an old, less engaged list.
Key considerations
- Maintain List Hygiene: Regularly clean your email lists by removing inactive, unengaged, or unverified subscribers to prevent spam reports.
- Verify Explicit Consent: Ensure all subscribers have given clear, explicit consent to receive your emails, avoiding purchased lists or the reactivation of old, unengaged segments.
- Audit Content and Frequency: Review your email content for relevance and align it with subscriber expectations. Assess sending frequency to prevent overwhelming recipients.
- Monitor Specific Campaigns: Identify and analyze particular campaigns or audience segments that may be contributing to the sudden increase in complaints.
- Offer Clear Unsubscribe: Always provide prominent and easy-to-use unsubscribe options in your emails to give recipients an alternative to reporting spam.
- Utilize Deliverability Tools: Leverage tools like Microsoft's Smart Network Data Services (SNDS) to verify actual increases in report rates and gain insights into sending behavior.
Marketer view
Marketer from Email Geeks explains that Microsoft's JMRPP complaints are processed through Mailgun for users of their service. He theorizes that Mailgun may have recently started forwarding these complaints to his webhooks, causing a sudden appearance of data previously unseen. He also verified an actual increase in report rates via SNDS and identified that this rise was linked to specific customer sending behavior.
22 Jun 2024 - Email Geeks
Marketer view
Marketer from Mailgun Blog explains that a high FBL complaint rate, such as with Microsoft's JMRP, is a clear sign that recipients are marking your emails as spam. A sudden increase usually means a significant portion of your recent sending is unwelcome, potentially due to sending to unengaged lists or an unexpected change in content.
1 Dec 2023 - Mailgun Blog
What the experts say
3 expert opinions
An unexpected surge in Microsoft's Feedback Loop complaint rates, as observed through your Mailgun account, primarily signals a critical issue within your sending practices rather than a fault with the platform itself. Experts consistently highlight that such elevated complaint rates are almost always the sender's responsibility, stemming from issues like mailing to old or unengaged lists, failing to secure explicit consent, or providing content that recipients find irrelevant or unexpected. While Mailgun simply reports these complaints from Microsoft's long-standing Junk Mail Reporting Program (JMRPP), the solution lies in thoroughly reviewing your list quality, content strategy, and sending frequency. Fluctuations in complaint data can also occur due to changes in reporting or customer sending behavior, but the core focus for resolution should remain on improving your email program's adherence to best practices and ensuring recipient satisfaction.
Key opinions
- Sender's Responsibility: High FBL complaint rates are almost always the direct result of the sender's email practices, such as poor list quality, lack of explicit consent, or irrelevant content, rather than an issue with the ESP.
- ESP as Reporter: Mailgun acts as a messenger for Microsoft's Feedback Loop data; it reports the complaints but is not the cause of the increased rate.
- JMRPP's Long History: Microsoft's Junk Mail Reporting Program (JMRPP), which feeds FBL data, has existed for many years, suggesting a new appearance of complaints might relate to reporting changes rather than the program itself being new.
- Engagement & Content Drive Complaints: Sending to old or unengaged lists, delivering irrelevant content, sending too frequently, or unexpected changes in sending volume are common causes of high complaint rates.
- Behavioral Fluctuations: Complaint rates can naturally fluctuate due to shifts in customer sending behavior, particularly for email SaaS providers.
Key considerations
- Prioritize List Health: Regularly clean and segment your email lists, focusing on highly engaged subscribers and ensuring all recipients have explicitly opted into your communications.
- Align Content & Frequency: Review your email content for relevance to your audience and adjust sending frequency to avoid overwhelming them, which can lead to increased complaints.
- Audit Sending Practices: Proactively audit your recent sending activities, including changes in list acquisition methods, audience segmentation, content themes, or sending volume, to identify potential triggers for the complaint surge.
- Provide Easy Opt-Out: Ensure your emails always include a clear, easy-to-find unsubscribe link, offering recipients a simple alternative to marking your messages as spam.
- Utilize Feedback Data: Use the FBL data reported by Mailgun to understand which campaigns or segments are generating complaints, allowing for targeted improvements.
Expert view
Expert from Email Geeks explains that Microsoft's Feedback Loop program, JMRPP, has existed since the mid-2000s, suggesting that a new appearance of complaints might be due to reporting changes rather than the program itself being new. She also notes that complaint data can be influenced by factors like mail being delivered to bulk folders, which prevents user complaints, and confirms that complaint rates can fluctuate due to customer sending behavior, especially for email SaaS providers.
13 Feb 2022 - Email Geeks
Expert view
Expert from Spam Resource explains that high complaint rates, including FBLs, are often caused by sending to old or unengaged lists, not delivering relevant content, sending too frequently, or experiencing unexpected changes in sending volume. He advises focusing on improving list quality, content relevance, and sending practices rather than blaming the ESP.
12 Jun 2025 - Spam Resource
What the documentation says
4 technical articles
A sudden spike in Microsoft FBL complaint rates reported through Mailgun points to underlying issues with your email sending program, often related to list quality or recent shifts in sending behavior. These complaints, originating from Microsoft's Junk Mail Reporting Program (JMRP), serve as a clear signal of recipient dissatisfaction and directly impair your sender reputation with Outlook.com and Exchange Online, leading to more aggressive filtering. Common causes include targeting old, unengaged, or unverified email addresses. While using shared IPs could mean other senders' actions contribute, the primary focus for resolution should remain on improving your own practices.
Key findings
- List Quality Decline: A key driver of increased Microsoft FBL complaints is often a decline in list quality, stemming from sending to old, unengaged, or unverified email addresses.
- Sender Reputation Harm: Elevated FBL complaint rates, particularly with Microsoft, directly indicate poor sender reputation, leading to stricter email filtering by their systems.
- Recipient Discontent: A surge in complaints signifies that recipients are actively marking your messages as junk because the content is unwelcome, unexpected, or uninteresting.
- Sending Practice Changes: Recent alterations in sending patterns, such as sudden volume increases or shifts in content, can trigger a spike in complaints.
- Shared IP Influence: For senders using shared IPs, the poor practices of other users on the same IP pool can inadvertently contribute to higher FBL complaint rates.
Key considerations
- Prioritize List Hygiene: Regularly clean your email lists by removing unengaged, old, or unverified addresses to maintain high quality and reduce the likelihood of complaints.
- Improve Engagement: Focus on re-engaging or removing inactive subscribers, concentrating your efforts on sending to those who actively interact with your emails.
- Strategic Sending: Segment your audiences and gradually increase sending volume to new or less engaged groups, avoiding sudden, large blasts that could lead to negative impacts on deliverability.
- Content Relevance: Ensure your email content is consistently relevant and aligns with subscriber expectations to minimize recipients marking messages as spam or junk.
- Monitor & Adapt: Continuously monitor Microsoft FBL rates and other deliverability metrics, adapting your sending strategies based on recipient feedback and performance data.
Technical article
Documentation from Mailgun explains that a sudden increase in FBL complaints, like those from Microsoft, often points to a decline in list quality or a recent change in sending practices, such as sending to old, unengaged, or unverified email addresses. They advise regularly cleaning lists and focusing on engaged subscribers.
1 Dec 2021 - Mailgun Documentation
Technical article
Documentation from Mailgun states that high FBL complaint rates, especially with Microsoft, are a direct indicator of poor sender reputation. If using shared IPs, this could be due to the actions of other senders. They recommend segmenting audiences and gradually increasing sending volume to avoid sudden negative impacts.
14 Jan 2023 - Mailgun Documentation
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