How accurate are SNDS colors in reflecting email delivery performance?
Matthew Whittaker
Co-founder & CTO, Suped
Published 27 May 2025
Updated 17 Aug 2025
8 min read
Microsoft's Smart Network Data Services (SNDS) is often a first stop for senders looking to gauge their reputation with Outlook.com. The platform presents your sending data in a color-coded format, typically using green, yellow, and red to signify different levels of trust and potential deliverability issues. It's natural to assume that a green status means your emails are sailing smoothly into inboxes, while yellow or red signals trouble. However, the accuracy of these colors in truly reflecting your email delivery performance is a more nuanced topic than it might initially appear.
While SNDS provides valuable insights into how Microsoft filters your mail, relying solely on its color indicators can be misleading. Email deliverability is a complex ecosystem, influenced by numerous factors beyond just the basic reputation signals. Understanding the limitations of SNDS colors is crucial for a comprehensive approach to maintaining good sender reputation and ensuring your messages reach their intended recipients.
Understanding SNDS color coding
The SNDS color system offers a quick overview of your IP's reputation with Microsoft. Green typically signifies a good reputation, indicating that most of your mail is accepted and delivered to the inbox. Yellow suggests a warning or a moderate level of spam filtering, meaning some of your mail might be going to the junk folder. Red indicates a poor reputation, with a significant portion of your mail likely being junked or blocked entirely. These colors are influenced primarily by a combination of complaint rates, spam trap hits, and engagement signals received by Microsoft's systems.
Specifically, Microsoft'sSender Support FAQ notes that more than 30% of IPs sending mail to Outlook.com maintain a complaint rate below 0.3%. This threshold can be considered a good benchmark for maintaining a green status. However, it's essential to remember that these colors are a snapshot and can change rapidly based on your sending behavior and recipient feedback.
It is important to acknowledge that the SNDS filter status (the color) largely represents the user's reaction to your content and mail stream, rather than a direct indicator of every email's journey to the inbox. While it factors in spam complaints, it doesn't give a full picture of all potential issues, such as soft bounces or throttling, which could still impact deliverability even if the color is green. The color system aims to provide a high-level reputation summary.
The nuance behind the colors
The main challenge with SNDS colors lies in their oversimplification of a very complex process. A green light in SNDS doesn't automatically mean 100% inbox placement. Microsoft, like other ISPs, uses hundreds of factors to determine where an email lands, including content, sender authentication (SPF, DKIM, DMARC), recipient engagement, and even the historical sending patterns from your IP and domain. The SNDS colors are just one piece of this puzzle. You might have a green status but still experience deliverability issues due to poor content quality or low engagement metrics from your recipients.
Another factor that can skew SNDS color accuracy is sending volume. If you're sending very low volumes of email, a small number of spam complaints or negative user reactions can disproportionately affect your SNDS color, pushing you into yellow or red territory. Conversely, if your volume is extremely low, Microsoft might not have enough data to build a comprehensive reputation profile for your IPs. This can lead to seemingly random color changes or inconsistencies, even with stable metrics like complaint rates.
For instance, a transactional sender with a consistently green SNDS status might still face deliverability challenges if their emails trigger other Microsoft filters based on content or infrastructure issues not explicitly reflected in the color. This can make troubleshooting particularly tricky, as the primary indicator suggests good health.
SNDS color interpretation
Green: Your IP has a good reputation, and emails are largely being delivered to the inbox.
Yellow: Your IP's reputation is moderate. Some emails may be sent to the junk folder.
Red: Your IP has a poor reputation, and many emails are likely being junked or blocked.
Practical implications for deliverability
Given the limitations, it's essential to integrate SNDS data into a broader deliverability strategy. While a green SNDS status is promising, it should never be your sole indicator of success. Always cross-reference it with other metrics and tools. For instance, if SNDS shows green but your campaigns are underperforming at Outlook.com, investigate other areas such as your content, sender authentication, or list hygiene. It's possible that your emails are hitting spam traps, even if not directly reflected in a color change.
A sudden shift to yellow or red, especially with low volume, might signal a specific issue with a recent campaign's content or audience. For example, sending a promotional email to a less engaged segment could trigger more complaints than usual, leading to a negative reputation shift. It's crucial to examine the specific sending patterns and content that preceded any color changes in SNDS. This can help you pinpoint the root cause of the issue.
Even with a green status during IP warming, you might not see the expected delivery uplift. This reinforces that Microsoft considers a wide array of signals. Your reputation isn't built on just one metric. It's a cumulative score based on ongoing interactions and adherence to best practices. Therefore, consistent monitoring of multiple data points is vital.
SNDS colors
Primary Indicator: Provides a general reputation snapshot based on Outlook.com's internal filtering.
Data Focus: Heavily weighted by user complaints and spam trap hits registered by Microsoft's systems.
Granularity: Daily, IP-specific reputation that can be volatile with low volumes.
Actual deliverability
Comprehensive View: Influenced by content quality, authentication (SPF, DKIM, DMARC), list hygiene, engagement metrics (opens, clicks, unsubscribes), and historical sending behavior.
Data Sources: Requires combining SNDS with seed list testing, ESP logs, and recipient engagement data.
Outcome Focus: Measures actual inbox placement rates, open rates, and conversion metrics.
Moving beyond color codes
To gain a truly accurate picture of your email delivery performance, you must look beyond the simplified color codes. Start by regularly monitoring your SNDS data, but don't stop there. Combine it with data from other sources to create a holistic view. This includes your Email Service Provider's (ESP) detailed sending logs, which provide information on bounces, deferrals, and other delivery outcomes. Analyzing these logs can reveal issues that SNDS colors might not highlight, such as throttling or temporary blocks that impact delivery without turning your SNDS status red.
Engagement metrics are also paramount. High open and click-through rates, coupled with low unsubscribe and complaint rates, signal healthy sender behavior to ISPs like Microsoft. If your SNDS is green but engagement is low, your emails might still be landing in the inbox but aren't resonating with recipients, which can eventually lead to reputation degradation. Implementing strong authentication protocols like SPF, DKIM, and DMARC also plays a critical role in your overall deliverability, contributing to a trustworthy sender identity.
Regularly review your reputation data from all available postmaster tools, not just SNDS. Furthermore, actively monitor for blacklisting (or blocklisting) on major DNSBLs, as a listing there can severely impact deliverability across all ISPs. While SNDS colors are a useful alert system, they are merely one indicator among many that contribute to your full deliverability picture.
Views from the trenches
Best practices
Maintain consistent sending volumes to help ISPs build a stable reputation profile for your IPs.
Regularly clean your email lists to remove inactive or invalid addresses, reducing bounce and complaint rates.
Monitor engagement metrics closely, as low engagement can negatively impact your sender reputation over time.
Segment your audience and tailor content to ensure relevance and prevent disinterest-based complaints.
Implement strong email authentication (SPF, DKIM, DMARC) for all sending domains.
Respond promptly to any sudden shifts in SNDS colors by investigating underlying causes like content or list issues.
Common pitfalls
Solely relying on SNDS colors to determine deliverability success can lead to missed issues.
Misinterpreting a green SNDS status as guaranteed inbox placement for all emails.
Ignoring low complaint rates that are still indicative of issues, especially with low sending volumes.
Failing to correlate SNDS data with other critical metrics like bounces, engagement, and spam trap hits.
Sending inconsistent email volumes, which can make reputation data appear volatile and unreliable.
Not adjusting email content or audience targeting in response to SNDS color changes or other negative signals.
Expert tips
For senders with high daily volumes, SNDS colors are often a more reliable indicator of spam percentage.
Consider SNDS colors as one data point in a comprehensive deliverability dashboard, not a standalone metric.
Low sending volumes can make SNDS colors appear random due to insufficient data for reputation profiling.
Even with a green SNDS status, it's crucial to check other factors like content and recipient engagement for true inbox placement.
A high complaint rate, even if not immediately reflected as red, will inevitably lead to delivery problems.
Spam trap hits, though not always changing the SNDS color, are a strong signal of list hygiene issues.
Expert view
Expert from Email Geeks says the SNDS colors are supposed to represent the user reaction to the message, meaning they are mostly content based, but sometimes they seem utterly random.
2024-10-20 - Email Geeks
Expert view
Expert from Email Geeks says that the filter color is mostly about content, and an IP can be green even with some complaints or spam trap hits.
2024-10-20 - Email Geeks
Getting the full picture
Ultimately, SNDS colors are a helpful, high-level indicator of your IP's reputation with Microsoft. They can alert you to potential issues like rising complaint rates or an increasing likelihood of your mail being filtered as junk. However, they do not provide a definitive measure of your actual inbox placement or overall email delivery performance. They are a signal, not the complete picture.
For a truly accurate understanding of your deliverability, combine SNDS data with comprehensive metrics from your ESP, engagement data, and regular monitoring for blacklists (or blocklists). This multi-faceted approach will provide the insights you need to optimize your email program and ensure your messages consistently reach the inbox.
Microsoft filters your mail, relying solely on its color indicators can be misleading. Email deliverability is a complex ecosystem, influenced by numerous factors beyond just the basic reputation signals. Understanding the limitations of SNDS colors is crucial for a comprehensive approach to maintaining good sender reputation and ensuring your messages reach their intended recipients.
Outlook.com's internal filtering.
Microsoft's systems.
