How to identify all Microsoft domains contributing to IP blocks in SNDS?
Matthew Whittaker
Co-founder & CTO, Suped
Published 28 Jun 2025
Updated 19 Aug 2025
7 min read
It can be frustrating when your IP address shows up as blocked in Microsoft's Smart Network Data Services (SNDS), especially if you believe you have suppressed all Microsoft domains from your sending lists. This situation often leads to confusion, as the immediate assumption is a misstep in segmentation or an unknown sending activity. However, the reality of Microsoft's email ecosystem is far more complex than just a handful of well-known domains like hotmail.com or outlook.com.
Many email senders find themselves in this predicament, seeing thousands of DATA commands in their SNDS logs despite having strict suppression rules in place. This scenario points to a crucial blind spot, the existence of numerous other Microsoft-associated domains that you might not be actively monitoring or suppressing. Understanding how to identify these domains is key to maintaining a clean sending reputation and ensuring your emails reach their intended recipients.
Uncovering all Microsoft domains that might be contributing to IP blocklists or blacklists in SNDS requires a methodical approach. It means looking beyond the obvious and delving into the intricacies of how Microsoft routes email for various services and regional domains. Let's explore how to get a clearer picture of these elusive domains and improve your deliverability to Microsoft inboxes.
Understanding Microsoft SNDS and IP blocks
Microsoft's Smart Network Data Services (SNDS) provides senders with data about their IP reputation and email traffic to Microsoft's consumer services, such as Outlook.com, Hotmail, and Live.com. Even if you're not explicitly sending to these primary domains, your IP can still be listed as blocked. This often happens because Microsoft's network encompasses a vast array of domains, many of which are not immediately obvious.
An IP can be added to a blocklist (or blacklist) in SNDS due to various factors, including high spam complaints, sending to spam traps, or unusual sending patterns detected by Microsoft's filters. If you see activity in SNDS for an IP you believe is suppressed, it indicates that mail is still reaching Microsoft's systems, either through unsuppressed domains or through misconfigured sending.
It's important to note that SNDS primarily monitors traffic to consumer-facing domains and does not typically reflect deliverability to Microsoft 365 hosted domains (formerly Office 365). This distinction is crucial, as many business emails are sent to these corporate domains, which operate under different filtering mechanisms. Therefore, an IP block in SNDS almost always relates to consumer mail traffic.
Accessing and understanding SNDS
SNDS provides critical insights into your sending reputation with Microsoft consumer mail services. To utilize it, you must request access for your IP addresses or IP ranges. Once approved, you can view data such as complaint rates, spam trap hits, and blocklist (or blacklist) status for your IPs. The data is usually presented in GMT, so adjust for your local timezone.
The hidden landscape of Microsoft domains
Beyond the common domains like hotmail.com, outlook.com, msn.com, and live.com, Microsoft handles mail for a vast network of international and older domains. These often include country-specific versions (e.g., hotmail.co.uk) and domains from previous acquisitions, like webtv.net. Many businesses and organizations also use Microsoft's Exchange Online for their email, though as mentioned, this doesn't directly contribute to SNDS data.
The key to identifying these additional domains lies in their MX records. Domains that route their email through Microsoft's infrastructure will point their MX records to Microsoft's mail exchange servers, typically ending in .olc.protection.outlook.com or .outlook.com. This is how Microsoft identifies incoming mail for its network, regardless of the user-facing domain name.
For example, a client database I reviewed included nearly 30 different domains that were routing through Outlook.com MX records, including various country-specific versions and lesser-known domains. This highlights that simply suppressing the four main domains is often insufficient.
Domain Category
Example Domains
Primary Consumer Domains
hotmail.com, outlook.com, live.com, msn.com. Typically point to *.olc.protection.outlook.com
International/Regional Domains
hotmail.co.uk, live.ca, outlook.es, and many more. These also use Microsoft's MX records.
Legacy/Acquired Domains
webtv.net, passport.com, windowslive.com. Some older domains may still route through mx*.hotmail.com
Strategies for identifying all contributing domains
To accurately identify all Microsoft domains your IP is sending to, the most reliable method is to examine your own email logs. Your logs contain precise recipient addresses, allowing you to cross-reference domains that receive mail from your IP with those whose MX records point to Microsoft. This is more accurate than relying on a predefined list, which may not be comprehensive or up-to-date.
Once you extract a list of unique domains from your mail logs, you can perform MX record lookups for each of them. This process helps you determine if a given domain uses Microsoft's mail infrastructure. Tools like MXToolbox or simple command-line utilities like nslookup or dig can be used for this. You're looking for MX records that contain terms like protection.outlook.com, outlook.com, or hotmail.com in their values. This approach helps you troubleshoot email deliverability issues effectively.
Example MX record lookupBASH
nslookup -type=MX hotmail.co.uk
While manually checking MX records for every domain in your list can be time-consuming, it is essential for a complete picture. This deep dive will reveal all the domains that funnel into Microsoft's network, giving you the ability to fine-tune your suppression lists or adjust your sending strategy accordingly. Neglecting this step can lead to persistent IP blocks (or blacklist entries) and poor email deliverability, even if your explicit Microsoft-domain sending is minimal.
Proactive monitoring and mitigation
Once you have a comprehensive list of all Microsoft-related domains your emails are reaching, proactive monitoring becomes vital. This means regularly reviewing your sending logs and MX records, as Microsoft's infrastructure can evolve, and new domains might be added or consolidated. Implement strict suppression processes for any unwanted traffic to these domains to avoid future blocklist (or blacklist) incidents.
Beyond domain identification, maintaining strong sending hygiene is crucial. This includes managing your email lists for high engagement, promptly removing unengaged subscribers, and avoiding sending to old or unverified addresses. These practices minimize the risk of hitting spam traps or generating high complaint rates, which are primary drivers for IP blocklisting (or blacklisting).
Utilizing deliverability tools and dashboards can significantly streamline this process. Many platforms offer insights into domain-specific deliverability and can help you identify anomalies in your sending patterns. Additionally, monitoring your DMARC reports can provide valuable information on unauthorized sending sources that might be using your domain, indirectly impacting your IP reputation with Microsoft and other ISPs.
Manual identification
Process: Requires extracting unique domains from your mail logs and performing individual MX lookups. This can be very time-consuming for large lists.
Accuracy: High, as it directly checks current MX records for domains you send to. However, it relies on the completeness of your log data.
Maintenance: Requires regular manual updates as email infrastructures and domain ownership can change, potentially leading to new Microsoft-routed domains.
Using a deliverability platform
Process: Automated analysis of your email traffic, often including categorization by ISP and domain, and real-time alerts on blocklists.
Accuracy: High, leveraging extensive data sets and continuous monitoring for comprehensive insights. This includes identifying unknown domains.
Maintenance: Minimal manual effort required, as the platform handles data collection, analysis, and updates. This frees up time for strategic adjustments.
Views from the trenches
Best practices
Regularly review your email sending logs to identify all unique recipient domains, not just the obvious ones.
Perform MX record lookups for all identified domains to confirm if they route through Microsoft's infrastructure.
Implement a robust suppression list that includes all identified Microsoft-owned domains to prevent sending to them if necessary.
Monitor your Microsoft SNDS data daily for any changes in IP reputation or new blocklist entries.
Maintain strong email hygiene practices to minimize spam complaints and spam trap hits.
Common pitfalls
Assuming only the major Microsoft domains (like Hotmail, Outlook) are relevant for suppression lists.
Failing to regularly update your domain lists, missing new or changed Microsoft-routed domains.
Not checking your mail logs thoroughly, leading to blind spots in your sending practices.
Ignoring low volumes of email traffic to Microsoft domains, which can still trigger blocklists over time.
Overlooking automated system sending that might be directed at Microsoft-affiliated addresses.
Expert tips
Consider automating the process of MX record lookups for your recipient domains if you send to a very large list.
Utilize internal deliverability dashboards that can filter and categorize domains by their MX records for easier identification.
Remember that SNDS data is in GMT, so align it with your local timezone for accurate analysis of sending patterns.
Even if not actively sending, old or dormant accounts on your list could trigger spam traps if they route to Microsoft's network.
Review Microsoft's official documentation for IP ranges and URLs to identify patterns in their network infrastructure.
Marketer view
Marketer from Email Geeks says checking if the SNDS data's GMT timezone helps explain unexpected activity should be the first step, though often it doesn't fully resolve the issue.
July 26, 2019 - Email Geeks
Marketer view
Marketer from Email Geeks says that many country-specific domains, like hotmail.co.uk, also route through Microsoft and should be accounted for in suppression lists.
July 26, 2019 - Email Geeks
Navigating Microsoft's email ecosystem
Identifying all Microsoft domains that contribute to IP blockages in SNDS is a nuanced but achievable task. It extends beyond the basic Hotmail or Outlook domains to include regional variants and legacy services, all identifiable through their MX records. By diligently analyzing your email logs, performing MX lookups, and adopting proactive monitoring strategies, you can gain a complete understanding of your email traffic to Microsoft's network. This comprehensive approach is essential for preventing unexpected IP blocklists (or blacklists), improving your deliverability rates, and ultimately ensuring your emails consistently land in the inbox.
Microsoft consumer mail services. To utilize it, you must request access for your IP addresses or IP ranges. Once approved, you can view data such as complaint rates, spam trap hits, and blocklist (or blacklist) status for your IPs. The data is usually presented in GMT, so adjust for your local timezone.
