Why does SNDS show blocked IPs with good acceptance rates and engagement?
Matthew Whittaker
Co-founder & CTO, Suped
Published 9 Jun 2025
Updated 16 Aug 2025
7 min read
It can be perplexing to see conflicting data when you're trying to ensure your emails reach the inbox. One common scenario that often raises eyebrows among email senders is when Microsoft's Smart Network Data Services (SNDS) reports an IP as blocked, yet your own metrics show excellent acceptance rates and strong recipient engagement. This discrepancy can make you question the validity of the data you're seeing.
Microsoft SNDS is designed to provide insights into the health of your sending IP addresses specifically as seen by Microsoft properties, such as Outlook and Hotmail. It's a critical tool for managing your sender reputation with Microsoft. However, the data isn't always as straightforward as it seems, and what appears to be a clear 'block' might not be a total cessation of delivery.
This article aims to unravel this puzzling situation. We'll explore why SNDS might show a blocked IP even when your emails are seemingly getting through, maintaining good acceptance rates, and generating positive engagement. Understanding these nuances is key to accurately interpreting your email deliverability performance and troubleshooting any underlying issues.
Understanding SNDS data and its interpretation
Microsoft SNDS provides a window into your email sending reputation with Microsoft properties. It offers data points like spam complaints, spam trap hits, and SmartScreen filter assessments, which are crucial for maintaining good deliverability. However, it's important to remember that SNDS is just one data source, and its reporting can sometimes be delayed or interpreted differently than a full block.
The 'blocked' status in SNDS might not always imply a hard block where all mail is rejected. It could indicate that the IP is listed on a less severe internal blocklist, or that a certain percentage of mail is being discarded or routed to the junk folder. This is why you might still see some mail accepted, especially if recipients are actively engaging with your content.
Furthermore, the color codes and status messages in SNDS, like 'blocked due to user complaints or other evidence of spamming,' are highly influenced by Microsoft's SmartScreen content filters. A red indicator doesn't automatically mean zero inboxing, just as a green indicator doesn't guarantee 100% inbox placement. The filter takes many factors into account, not just the IP reputation.
Why contradictions in SNDS reports arise
Several factors can contribute to the puzzling scenario of a blocked IP in SNDS while your email acceptance and engagement metrics remain robust. One significant reason is the inherent delay in data reporting within SNDS.
Microsoft's systems are constantly evaluating incoming mail streams, and reputation changes can happen quickly. However, these changes might not be reflected instantaneously in your SNDS dashboard. It's possible that an issue caused a temporary block (or blacklist) listing, which then cleared up, but the SNDS portal has yet to update its status. This latency can create a misleading impression.
Another crucial aspect is Microsoft's granular filtering system. An IP might be 'blocked' for certain types of mail (e.g., promotional content) or for specific segments of recipients who have previously marked your mail as spam, while transactional or highly engaged recipients continue to receive your emails. This micro-segmentation of filtering decisions means a general 'blocked' status in SNDS doesn't necessarily mean a blanket block for all your mail. To gain further insight, consider reading our article, Why is SNDS reporting all green IPs with no delivery uplift?.
Beyond SNDS: broader deliverability factors
While SNDS provides valuable data, it's crucial to remember that it's only one piece of the intricate email deliverability puzzle. Your overall sender reputation goes beyond what SNDS reports.
Factors like your domain reputation, content quality, and consistent authentication (SPF, DKIM, DMARC) play a massive role in whether your emails land in the inbox or the spam folder. If these elements are strong, they can sometimes mitigate the impact of a minor IP-level block (or blacklist) indicated by SNDS. You can learn more about this by reading our guide to DMARC, SPF, and DKIM.
High engagement metrics, such as opens, clicks, and replies, are incredibly powerful signals to mailbox providers like Outlook. If your subscribers are consistently interacting positively with your emails, this can often override negative signals from an IP being flagged in SNDS. Engaged users can essentially 'pull' your emails into the inbox, even if there's a minor reputation concern at the IP level.
Microsoft also utilizes various internal, dynamic blocklists (or blacklists) that aren't publicly disclosed or immediately reflected in SNDS. These internal lists can cause delivery issues even if SNDS looks clear. Spam trap hits, for example, can trigger these hidden filters without always resulting in a clear 'blocked' status in SNDS.
Diagnosing and addressing the discrepancy
When you encounter this paradox, the first step is to avoid panic. Start by cross-referencing your SNDS data with other crucial deliverability metrics.
Check your bounce logs for specific error codes from Microsoft. Are you seeing S3140 or other block-related codes? If not, it strengthens the case for a potential SNDS reporting anomaly. Also, monitor your spam complaint rates and inbox placement through seeding tests. These provide a more real-time view of your current deliverability status. It's also worth noting that it's possible to resolve Microsoft email blocks even when SNDS appears normal.
If the discrepancy persists and you're concerned, it can be beneficial to review your sending practices. Have there been any recent changes to your email volume, content, or list acquisition methods? Sometimes, even minor shifts can trigger reputation flags. Ensuring your list hygiene is impeccable and your content is relevant and engaging is always the best long-term strategy.
Finally, if you've done your due diligence and the SNDS reporting still seems off, don't hesitate to reach out to Microsoft's sender support. Sometimes, the issue might indeed be a glitch on their end, or they can provide a more nuanced explanation for the 'blocked' status that isn't immediately obvious from the SNDS portal.
Views from the trenches
Best practices
Maintain exceptional list hygiene to avoid spam traps and inactive addresses, which are primary drivers of IP blacklisting.
Consistently monitor multiple deliverability metrics, not just SNDS, to get a holistic view of your sender reputation.
Segment your audience and tailor your content to maintain high engagement, which positively influences deliverability.
Implement strong email authentication protocols, including SPF, DKIM, and DMARC, to verify your sending identity.
Common pitfalls
Over-relying solely on SNDS 'green' status as a guarantee of perfect deliverability.
Ignoring subtle bounce codes or low engagement for specific segments while overall metrics seem fine.
Making rapid, drastic changes to email volume or content without gradual testing.
Failing to regularly clean your email lists of unengaged or invalid contacts.
Expert tips
When SNDS shows a block but deliverability is good, it could be a transient issue or a granular filter that doesn't affect all mail.
Engaging with Microsoft support directly can sometimes provide clarity on conflicting SNDS reports.
A high acceptance rate might mask underlying issues if a significant portion of mail is still landing in junk folders.
Remember that Microsoft's systems are dynamic; ongoing monitoring and adaptation are key to sustained inboxing.
Marketer view
Marketer from Email Geeks says they had a similar issue where an IP showed as blocked, but Microsoft support confirmed no delivery issues, suggesting a possible glitch.
2022-03-01 - Email Geeks
Marketer view
Marketer from Email Geeks says the color codes in SNDS are more reflective of what SmartScreen content filters think of the mail, not a definitive block for all email delivery.
2022-03-02 - Email Geeks
Navigating SNDS data anomalies
The discrepancy between a 'blocked' status in Microsoft SNDS and positive deliverability metrics can be unsettling, but it's often a nuanced situation rather than a clear red flag. SNDS is a powerful tool, yet its data should be contextualized within your broader email program's performance.
Factors like data reporting delays, the granularity of Microsoft's filtering, and the overarching influence of your sender reputation and audience engagement all play a role. By monitoring a comprehensive set of metrics and being proactive in your email practices, you can navigate these apparent contradictions effectively.
Ultimately, if your emails are reaching the inbox, being accepted, and driving engagement despite a concerning SNDS status, it might indicate a temporary system anomaly or a less severe issue that isn't impacting your core deliverability. Continuous vigilance and a holistic approach to email deliverability are your best defenses against such paradoxes.
Outlook. If your subscribers are consistently interacting positively with your emails, this can often override negative signals from an IP being flagged in SNDS. Engaged users can essentially 'pull' your emails into the inbox, even if there's a minor reputation concern at the IP level.
