Why does Microsoft SNDS data contradict email deliverability during IP warming?
Michael Ko
Co-founder & CEO, Suped
Published 18 May 2025
Updated 19 Aug 2025
10 min read
It is a common scenario that can leave even seasoned email marketers scratching their heads. You are in the midst of IP warming, carefully increasing your sending volume, and meticulously monitoring your deliverability metrics. Your Microsoft Smart Network Data Services (SNDS) portal shows a pristine green or stable yellow reputation, indicating all systems are go. Yet, your internal engagement metrics, particularly open rates for Microsoft recipients, tell a different story, often hovering near zero. This stark contradiction can be incredibly frustrating and confusing.
Why does Microsoft SNDS data appear to contradict your actual email deliverability during IP warming? The core issue lies in understanding what SNDS truly reports versus the nuanced complexities of inbox placement. SNDS primarily indicates whether Microsoft is accepting your email, not necessarily where it lands in the recipient's mailbox. During IP warming, new IP addresses are often viewed with suspicion by Internet Service Providers (ISPs), including Microsoft, until they establish a positive sending reputation.
This guide will delve into why this discrepancy occurs and what actionable steps you can take to get a clearer picture of your deliverability to Microsoft properties like Outlook.com. We will explore the limitations of SNDS, the factors that truly influence inbox placement, and best practices for navigating the challenging but crucial IP warming phase. Understanding these dynamics is essential for ensuring your legitimate emails reach their intended audience, rather than being silently filtered into the junk folder or blocked outright.
Understanding Microsoft SNDS during IP warming
Microsoft Smart Network Data Services, or SNDS, is a free portal provided by Microsoft, designed to give senders insights into their IP reputation and email activity. It tracks key metrics like email volume, complaint rates, and spam trap hits for registered IP addresses. The portal uses a color-coded system (green, yellow, red) to indicate the overall health of your sending IP, with green signifying a good reputation and red indicating significant issues or blockages. You can also view the total number of recipients your mail was accepted for (rcpt/data).
During IP warming, a new IP address begins with no established reputation. ISPs, including Microsoft, are inherently cautious of unknown senders to prevent spam. This means that initially, a significant portion of your emails might be directed to the junk folder or experience silent filtering, even if your SNDS status appears positive. The green or yellow status in SNDS primarily reflects Microsoft's willingness to accept your mail, not its placement in the inbox.
A key limitation of SNDS is that it only displays data that directly affects delivery to Microsoft inboxes. This means if your emails are being filtered to the junk folder, it might not be explicitly flagged as a negative reputation issue within SNDS itself. The system is more focused on preventing unwanted mail from reaching Microsoft servers rather than providing granular inbox placement diagnostics for mail that has been accepted. For more details, you can refer to the SNDS FAQ page on Microsoft's sender support site.
Therefore, even with a seemingly good SNDS status, it is critical to rely on additional metrics and data sources to accurately assess your inbox placement during the sensitive IP warming period. For further reading, consider how accurate is Microsoft SNDS data for deliverability monitoring in general.
Why the data contradiction occurs
The primary reason for the contradiction is the distinction between email acceptance and inbox placement. When SNDS shows your IP as green, it means Microsoft mail servers are accepting your mail for delivery. However, this acceptance does not guarantee that the email will land in the primary inbox. It could still be routed to the junk folder, promotions tab, or even silently dropped, leading to the observed low open rates without explicit bounces.
Microsoft's filtering system is sophisticated and relies on hundreds of signals, not just the IP reputation reflected in SNDS. During IP warming, even with a clean IP, other factors might trigger spam filters, such as: unfamiliar sending patterns, low initial engagement from recipients, a high ratio of unengaged recipients, or content that appears suspicious to Microsoft's algorithms. This often leads to new IPs experiencing high junk rates.
Another factor contributing to the discrepancy is Microsoft's tendency towards silent filtering. This means that mail may be accepted by the server but immediately dropped or routed to junk without generating a bounce message. If your ESP is not properly capturing these nuanced delivery responses, your internal bounce rates might appear low, while actual inbox placement remains poor. This issue is particularly frustrating during the crucial initial stages of an IP warm-up.
Metric
SNDS Indication
Actual Impact during IP Warming
IP Status
Green/Yellow
Emails accepted, but often junked or silently dropped.
Email Volume
High rcpt/data
Low open rates, high junk folder placement.
Complaint Rate
Low
Might be low because emails aren't reaching inboxes to be complained about.
Bounce Rate
Low
Silent filtering can lead to fewer explicit bounces.
Key factors influencing Microsoft deliverability
Beyond what SNDS reports, several critical factors heavily influence whether your emails land in the inbox during IP warming. The foundational element is email authentication. Properly configured SPF, DKIM, and DMARC records are non-negotiable for establishing trust with Microsoft's filters. These protocols verify that your emails are legitimately from your domain and haven't been tampered with.
Sender reputation, which is a broader concept than just IP reputation, also plays a massive role. This includes the quality of your email content (avoiding spammy keywords, broken links, or overly promotional language), your list hygiene practices (removing inactive users, avoiding spam traps), and critically, recipient engagement. During warm-up, sending to highly engaged subscribers is paramount, as positive interactions (opens, clicks, replies) signal to Microsoft that your mail is wanted. Conversely, low engagement or high complaint rates, even if not immediately reflected as a red flag in SNDS, will quickly degrade your overall sender reputation and lead to poor inbox placement.
Furthermore, consistent sending volume and frequency are essential. Erratic sending patterns or sudden spikes in volume can trigger Microsoft's filters. It is important to remember that Microsoft may employ various filtering stages, from soft bounces and rate limiting to outright blocklisting (or blacklisting), and eventually even router blocking, without always providing explicit feedback in SNDS. This makes a multi-faceted approach to monitoring and troubleshooting critical.
List hygiene: Regularly clean your lists to remove inactive or invalid addresses, reducing bounces and spam trap hits.
Engagement: Send only to engaged subscribers. Low engagement signals can quickly degrade your reputation.
Content quality: Avoid spammy keywords, broken links, or overly promotional content that triggers filters.
Strategies to resolve the contradiction
To effectively address the contradiction between Microsoft SNDS and actual inbox placement, you need a multi-pronged strategy. First, do not rely solely on SNDS. While it provides valuable insights into your IP's acceptance status, it should be complemented by your own sending data, particularly open and click rates, for a true picture of inbox delivery. If your open rates to Microsoft recipients are low, it is a strong indicator of filtering, regardless of your SNDS status.
Second, proactive communication with Microsoft can sometimes help. Using their dedicated sender support form to inform them of your new IPs and anticipated sending volumes before you begin warming can occasionally ease initial filtering. While not a guaranteed fix, it signals your legitimate intent and provides Microsoft with context about your sending practices. For those experiencing issues, Microsoft's own forums sometimes discuss SNDS data insights.
Third, meticulously analyze your bounce logs and server responses. If Microsoft is rate limiting you, you should see specific soft bounce codes. If you are not seeing explicit bounces but low engagement, it suggests silent filtering. In such cases, you might need to pull back your sending volumes even further than initially planned and focus intensely on engaging only your most active recipients. Consider also how to troubleshoot Microsoft email deliverability issues and analyze SNDS data more deeply.
Proactive steps
Reach out to Microsoft sender support to inform them of your new IPs and expected sending volumes before starting warm-up. This can sometimes ease initial filtering.
Reactive monitoring
Actively monitor your bounce logs and analyze SMTP error codes for signs of rate limiting or specific blocks. You can learn more about this by reading: Why dedicated IPs are red in SNDS.
Rely on actual engagement metrics, like open and click rates, as the primary indicators of inbox placement, rather than solely on Outlook.com SNDS colors.
Navigating IP warming with Microsoft
While Microsoft SNDS is a useful tool for monitoring the basic health of your sending IPs, it's crucial to understand its limitations during IP warming. The green or yellow status in SNDS indicates acceptance by Microsoft's mail servers, not guaranteed inbox placement. New IPs are initially treated with caution, often resulting in silent filtering to the junk folder, which SNDS may not explicitly highlight as a reputation issue.
To gain a comprehensive understanding of your deliverability, especially during IP warming, you must look beyond SNDS alone. Prioritize email authentication (SPF, DKIM, DMARC), maintain rigorous list hygiene, focus on sending to highly engaged recipients, and ensure consistent, gradual sending volumes. Critically, monitor your internal open rates, click-through rates, and analyze detailed bounce logs from your ESP.
By combining the insights from SNDS with your own engagement metrics and proactively managing your sender reputation, you can more accurately assess your progress during IP warming and take timely corrective actions. This holistic approach is key to achieving optimal inbox placement with Microsoft and ensuring your messages reach their intended audience effectively.
Views from the trenches
Best practices
Always monitor a broad range of deliverability metrics, not just SNDS data.
Proactively communicate with Microsoft about your IP warming plans.
Consistently maintain high email quality and engage only with active subscribers.
Common pitfalls
Solely trusting SNDS reputation colors as a definitive indicator of inbox placement.
Ignoring low open rates, assuming SNDS 'green' status means good deliverability.
Neglecting bounce logs, which might reveal hidden rate limiting or silent blocks.
Expert tips
Integrate data from multiple sources like your ESP's reports and engagement metrics for a holistic view.
Understand that new IPs are "guilty until proven innocent" by ISPs, leading to initial junking.
Recognize that Microsoft's filtering is dynamic and considers many factors beyond basic IP reputation.
Expert view
Expert from Email Geeks says: There is a difference between accepting email and inbox placement. When warming up IPs, you can expect nearly 100% spam placement at Microsoft.
2019-11-12 - Email Geeks
Marketer view
Marketer from Email Geeks says: The SNDS colors are not entirely reliable, and you should not solely depend on them.
Microsoft Smart Network Data Services (SNDS) portal shows a pristine green or stable yellow reputation, indicating all systems are go. Yet, your internal engagement metrics, particularly open rates for Microsoft recipients, tell a different story, often hovering near zero. This stark contradiction can be incredibly frustrating and confusing.
Outlook.com SNDS colors.
