Why is SNDS down and are Outlook inboxing rates affected?
Michael Ko
Co-founder & CEO, Suped
Published 19 Jul 2025
Updated 16 Aug 2025
8 min read
Microsoft's Smart Network Data Services (SNDS) is a critical tool for email senders, offering insights into how their emails are being handled by Outlook.com and other Microsoft mailboxes. It provides data on sender reputation, complaint rates, and spam trap hits, which are all vital for maintaining good deliverability. However, there are times when SNDS experiences downtime or data inconsistencies, leaving senders in the dark and potentially impacting their inbox placement.
When SNDS is not providing data, it can cause significant anxiety for email marketers and deliverability professionals. The lack of transparency makes it challenging to diagnose issues and confirm whether email campaigns are reaching their intended recipients' inboxes or ending up in spam folders. This uncertainty can lead to panic, especially for those who rely heavily on SNDS metrics for day-to-day operations and troubleshooting.
Why SNDS data issues occur
SNDS downtime or data issues are not uncommon. Users frequently report periods where the portal shows no data, or data is significantly delayed. This can be due to various factors, from maintenance windows on Microsoft's end to technical glitches that prevent data from being processed and displayed accurately. Sometimes, these issues are temporary and resolve on their own, while other times they persist for days, causing considerable concern among senders.
One specific issue that has been reported by users, especially those using email service providers (ESPs) like Salesforce Marketing Cloud, is the revocation of authorization for IPs in SNDS. This means that even if SNDS is technically operational, a sender might not see their data because access has been inadvertently or intentionally revoked. This highlights that SNDS data issues aren't always about the system being down, but also about access permissions.
Another common scenario involves minimum thresholds. SNDS requires a certain volume of emails to be sent from an IP address before it can collect and display data. If your sending volume drops, or if you're a low-volume sender, you might see empty data sets even when the service is functioning normally for high-volume senders. This isn't a downtime issue, but rather a data limitation that can be misinterpreted as one.
Understanding SNDS data limitations
While SNDS is valuable, it's essential to understand its scope and limitations. It provides a snapshot of your sending reputation with Microsoft, but it doesn't offer real-time data or cover every aspect of email delivery. Many factors outside of SNDS's reported metrics can influence inbox placement.
A common misconception is that a green status in SNDS guarantees inbox placement. This is not always the case. Even with positive SNDS metrics, emails can still land in spam or be blocked due to other factors like content, recipient engagement, or a broad range of internal Microsoft filtering rules not directly exposed in SNDS.
Impact on Outlook inboxing rates
When SNDS is down or showing no data, it's natural to worry about Outlook inboxing rates. Anecdotal evidence from deliverability professionals suggests that indeed, a drop in Outlook inboxing can sometimes coincide with SNDS outages or data issues. Senders have reported significant drops, sometimes over 20%, in their inbox placement rates to Outlook.com and related domains (Hotmail, Live) during periods when SNDS data was unavailable. This doesn't necessarily mean SNDS downtime *causes* poor deliverability, but it certainly removes a key monitoring tool just when it's needed most.
The correlation could be coincidental, with underlying deliverability problems surfacing just as the monitoring tool becomes unavailable. Or, it could suggest a deeper systemic issue within Microsoft's email ecosystem that affects both SNDS data reporting and email filtering simultaneously. Regardless, the lack of data exacerbates the problem, making it harder to pinpoint the root cause of declining inbox rates.
It's important to remember that Microsoft, like other major mailbox providers (Gmail, Yahoo), uses a complex array of factors to determine inbox placement. These include sender reputation, spam complaints, bounce rates, authentication (SPF, DKIM, DMARC), and user engagement. While SNDS provides insight into some of these, it doesn't tell the whole story. A sudden drop in inboxing could be due to a recent change in your sending practices, list quality, or even a shift in Microsoft's filtering algorithms. This makes it crucial to rely on multiple data points for a holistic view of your deliverability, especially when one tool is offline.
Factor
Impact on deliverability
SNDS coverage
Sender reputation
Overall trust score, influenced by engagement and compliance.
Provides IP reputation (color-coded).
Spam complaint rate
High rates indicate unwanted mail, leading to blocklisting or spam folder placement.
Reports complaint rates per IP.
Bounce rate
High rates suggest poor list hygiene, negatively affecting reputation.
Indirectly, via IP reputation metrics.
Email authentication
SPF, DKIM, and DMARC prevent spoofing and build trust, crucial for deliverability.
SNDS does not directly report on authentication passes/fails.
User engagement
Opens, clicks, and replies signal legitimate interest, improving sender standing.
Not directly measured by SNDS, but influences spam complaint rates.
Diagnosing deliverability issues without SNDS
When SNDS is unavailable, it becomes even more critical to rely on other methods to diagnose and troubleshoot deliverability issues. This means looking beyond Microsoft's specific tool and focusing on universal email best practices and alternative monitoring solutions.
One of the most immediate steps is to check your email service provider's (ESP) internal delivery reports. Most ESPs provide their own metrics on bounce rates, complaint rates, and open/click rates. While these may not be specific to Outlook.com, they can give you a general idea of your campaign performance and highlight any sudden drops across all mailbox providers. If you see a decline across the board, the issue might be with your sending practices rather than Microsoft specifically. You can also send test emails to various mailbox providers, including Outlook, and monitor where they land using an inbox placement tool.
Another crucial step is to check external email blocklists (blacklists). Being listed on a major blocklist can severely impact your deliverability to all providers, including Outlook. Many free online tools allow you to check if your IP addresses or domains are listed. If you find yourself on a blocklist (or blacklist), immediate action is required to request delisting and address the underlying cause of the listing. This often involves reviewing your sending practices, list hygiene, and content.
Symptoms of a problem
Sudden drop: Unexplained decrease in open or click rates, particularly with Outlook recipients.
Increased bounces: Higher than usual bounce rates, especially soft bounces indicating temporary blocks.
Spam folder placement: Reports from subscribers that your emails are going to their spam or junk folders.
Actions to take
Review logs: Examine your mail server logs for specific error messages from Microsoft, such as rate limits or rejections.
Check Microsoft's support forums: Look for other senders reporting similar issues, which might indicate a broader problem or update from Microsoft.
Maintaining optimal Outlook deliverability
Regardless of SNDS's status, proactive measures are key to maintaining strong Outlook deliverability. These practices are fundamental to good email hygiene and reputation management, and they will serve you well even when your primary monitoring tools are experiencing issues.
First, prioritize list hygiene. Regularly clean your email lists to remove inactive or invalid addresses. High bounce rates signal to mailbox providers that your list quality is poor, which can negatively impact your sender reputation. Implement double opt-in for new subscribers to ensure they genuinely want to receive your emails, reducing the likelihood of spam complaints and improving engagement. Focusing on quality over quantity is essential for long-term deliverability.
Second, pay close attention to email content and engagement. Avoid spammy keywords, excessive images, or broken links. Craft compelling subject lines and relevant content that encourages opens and clicks. Microsoft, like other providers, heavily weighs user engagement in its filtering decisions. Low engagement can lead to emails being sent to the junk folder, even if technical authentication is perfect. Ensuring your messages are well-received will contribute to a positive sender reputation and better inbox placement. Also, make sure to comply with Outlook's new sender requirements for high-volume senders, which emphasize strong authentication and low complaint rates.
While SNDS downtime can be frustrating, it shouldn't derail your email program. By focusing on robust authentication, diligent list hygiene, and engaging content, you can mitigate the risks associated with unreliable monitoring data. Remember that email deliverability is a multi-faceted challenge that requires a holistic approach, not just reliance on a single tool. Understanding all the factors that influence deliverability is essential for long-term success.
When facing deliverability challenges, consider them an opportunity to review and strengthen your overall email strategy. By implementing best practices and continuously monitoring your performance through various channels, you can build a resilient email program that thrives even when tools like SNDS experience temporary glitches. Consistency and adherence to best practices are the ultimate keys to ensuring your emails reach the inbox.
Views from the trenches
Best practices
Always maintain strong email authentication (SPF, DKIM, DMARC) for all sending domains.
Segment your email lists and send targeted content to improve engagement and reduce complaints.
Regularly clean your subscriber lists to remove inactive or bouncing email addresses.
Common pitfalls
Over-reliance on a single monitoring tool like SNDS for all deliverability insights.
Ignoring low engagement rates, which can silently degrade your sender reputation.
Not monitoring external IP blocklists (blacklists) during SNDS downtime.
Expert tips
Use an inbox placement testing tool to monitor where your emails land across major mailbox providers.
Review mail server logs for specific error codes or throttling messages from Microsoft.
Engage with the email community on forums to stay updated on widespread deliverability issues.
Marketer view
Marketer from Email Geeks says they were seeing errors all day in SNDS, indicating a potential widespread issue.
2021-06-18 - Email Geeks
Marketer view
Marketer from Email Geeks says that for them, the SNDS data had been empty for the past two days.
Salesforce Marketing Cloud, is the revocation of authorization for IPs in SNDS. This means that even if SNDS is technically operational, a sender might not see their data because access has been inadvertently or intentionally revoked. This highlights that SNDS data issues aren't always about the system being down, but also about access permissions.
(Gmail, Yahoo), uses a complex array of factors to determine inbox placement. These include sender reputation, spam complaints, bounce rates, authentication (SPF, DKIM, DMARC), and user engagement. While SNDS provides insight into some of these, it doesn't tell the whole story. A sudden drop in inboxing could be due to a recent change in your sending practices, list quality, or even a shift in Microsoft's filtering algorithms. This makes it crucial to rely on multiple data points for a holistic view of your deliverability, especially when one tool is offline.
Microsoft, such as rate limits or rejections.
