What Microsoft domains should I exclude from my email segmentation?
Matthew Whittaker
Co-founder & CTO, Suped
Published 11 May 2025
Updated 15 Aug 2025
7 min read
Managing email segmentation effectively is crucial for maintaining good sender reputation and ensuring your messages land in the inbox. A common challenge arises when dealing with Microsoft domains, as their ecosystem includes a wide array of consumer and corporate email services. Understanding which domains to exclude from your email segmentation can prevent unnecessary bounces, improve deliverability metrics, and enhance the overall health of your email program.
When reviewing your email deliverability to Microsoft accounts, you might notice traffic even when you believe you've excluded all Microsoft domains. This often indicates that your exclusion list isn't comprehensive enough. We need to look beyond the obvious consumer domains like Outlook and Hotmail to capture all traffic destined for Microsoft's mail servers.
Excluding the right domains helps you focus your email efforts on audiences that are more likely to engage, preventing your IP address from being impacted by deliverability issues or even landing on a blacklist. Let's explore the various types of Microsoft-related domains you should consider for your exclusion lists.
Identifying primary consumer domains
When you think of Microsoft email accounts, the first domains that come to mind are usually the free consumer email services. These are fundamental to any exclusion strategy for Microsoft domains. It's not just the primary top-level domains, but also their country-specific variations.
The most common domains to include in your initial exclusion filter are:
Hotmail: This classic email service includes @hotmail.com, as well as numerous country-specific versions like @hotmail.co.uk, @hotmail.fr, etc.
Outlook: The more modern free email service, encompassing @outlook.com and its localized variations like @outlook.co.uk or @outlook.fr.
Live: Part of the older Windows Live branding, including @live.com and its international equivalents.
MSN: Another legacy domain, @msn.com.
To ensure comprehensive coverage, it's best to use a wildcard exclusion for these domains. For example, rather than listing every hotmail. variation, a filter like 'hotmail%' or '%hotmail.%' can capture all country-code top-level domains (ccTLDs) associated with Hotmail.
Considering office 365 and non-obvious domains
Beyond the well-known consumer domains, many organizations, including educational institutions and businesses, use Microsoft 365 (formerly Office 365) for their email hosting. While these companies use their own custom domains (e.g., @yourcompany.com), their mail is still routed through Microsoft's infrastructure.
To effectively exclude these, you need to identify the Mail eXchanger (MX) records that point to Microsoft servers. These often contain terms like protection.outlook.com or mail.outlook.com. Some older configurations might still point to pamx1.hotmail.com.
Several domains that don't appear to be Microsoft-owned on the surface actually route their email through Microsoft's servers. For instance, domains like dbmail.com, dartybox.com, and netcabo.pt have been observed to use Hotmail or Outlook MX records. Including these in your exclusion list can prevent unintended sends. You can use a tool to check the MX records for domains you suspect might be routing through Microsoft owned inboxes for exclusion.
Example of a comprehensive exclusion filterSQL
AND Domain_ not like '%hotmail.%'
AND Domain_ not like '%outlook.%'
AND Domain_ not like '%live.%'
AND Domain_ not like '%msn.%'
AND MX_Record_ not like '%protection.outlook.com%'
AND MX_Record_ not like '%mail.outlook.com%'
AND MX_Record_ not like '%pamx1.hotmail.com%'
The importance of exclusion for deliverability
Excluding certain Microsoft domains isn't just about reducing traffic. It's a strategic move that significantly impacts your overall email deliverability. Every email sent, especially those that result in negative engagement, contributes to your sender reputation.
By proactively excluding domains that are prone to spam traps or have historically low engagement, you are protecting your sending infrastructure. When your emails are sent to irrelevant or unengaged Microsoft accounts, it can lead to higher complaint rates and increase the likelihood of your IP address or domain being placed on a blacklist (or blocklist). This can then affect your ability to reach all recipients, not just those at Microsoft.
The impact of not excluding
Increased Complaints: Sending to unengaged Microsoft accounts often results in higher spam complaints.
Furthermore, a robust exclusion strategy contributes to maintaining a cleaner email list, reducing the chances of hitting spam traps or sending to invalid addresses. This, in turn, helps maintain a healthy list compliance score and improves the accuracy of your engagement metrics.
Implementation and best practices
Implementing an effective domain exclusion strategy requires careful attention to detail and ongoing monitoring. Simply listing a few common domains might not be enough to capture all the email traffic that routes through Microsoft's infrastructure.
First, ensure your segmentation logic is robust. Using wildcard characters (% or * depending on your system) is critical for catching all variations, including ccTLDs and subdomains. For instance, '%outlook.%' will exclude outlook.com, outlook.co.uk, and others. Additionally, regularly review your bounce logs for unexpected Microsoft-related domain activity.
Consider the nuances of Microsoft's email filtering and their various MX records. For example, some domains might look independent but are actually hosted by Microsoft, as evidenced by their MX records pointing to Microsoft's servers. Keeping an eye on these helps refine your exclusion list, preventing you from sending to addresses that Microsoft might perceive negatively.
Shared responsibility domains (SRDs)
One area where this becomes particularly complex is with Shared Responsibility Domains (SRDs). These domains are often associated with web hosting providers or smaller ISPs that use Microsoft's email infrastructure. While they might appear as unique domains, their reputation and deliverability can be tied back to Microsoft's broader systems. This is why SRD votes can impact email reputation.
Understanding SRDs
Shared Responsibility Domains are domains where the primary MX records point to Microsoft's mail exchange servers (e.g., protection.outlook.com). This means that even if the domain isn't microsoft.com, hotmail.com, etc., email deliverability to it is largely controlled by Microsoft's reputation filters.
Identifying SRDs
While there isn't a public, exhaustive list of all SRDs, you can identify them by performing MX record lookups for suspicious domains in your list. If the MX record points to a Microsoft domain, then that email address will be processed by Microsoft, and any deliverability issues with Microsoft will affect it.
Excluding these implicit Microsoft-bound domains can further refine your segmentation, ensuring your efforts are directed towards recipients that offer the best engagement potential. This can also help in adhering to company policy or specific internal guidelines for email sending.
Conclusion
Excluding Microsoft domains from your email segmentation is a proactive measure to safeguard your sender reputation and optimize deliverability. It's not just about removing @outlook.com or @hotmail.com addresses, but also about identifying and accounting for domains that route through Microsoft's mail infrastructure.
Regularly reviewing your email logs, monitoring bounce reasons, and staying informed about changes in MX records can help you maintain an accurate exclusion list. This continuous effort will contribute to a healthier sending reputation, higher inbox placement rates, and more effective email campaigns. By refining your segmentation, you ensure that your valuable messages reach the intended recipients without being caught in unnecessary filters or routed to the spam folder.
Views from the trenches
Best practices
Actively monitor your bounce logs and Sender Score reports for any unexpected Microsoft-related activity.
Implement a tiered exclusion strategy, starting with broad wildcard matches for common consumer domains.
Regularly update your exclusion lists to account for new domains routing through Microsoft infrastructure.
Common pitfalls
Only excluding basic domains like Outlook.com, Hotmail.com, Live.com, and MSN.com.
Ignoring the MX records of custom domains that route through Microsoft 365 or Outlook Protection.
Not using wildcard characters in exclusion rules, leading to missed country-specific or subdomain variations.
Expert tips
When analyzing email logs, pay close attention to the MX records of recipient domains. If they point to Microsoft's servers, such as `protection.outlook.com` or `mail.outlook.com`, consider excluding these domains if they don't align with your target audience.
For dynamic exclusion, consider scripting a process that regularly checks MX records of domains in your list and automatically adds Microsoft-routed domains to your exclusion list.
If you're seeing unexpected traffic in SNDS, look for domains that might have recently migrated to Microsoft 365 or acquired by Microsoft, as these might not be on your current exclusion list.
Expert view
Expert from Email Geeks says: SNDS complaint samples are typically only available for a week, after which the links expire and may return a blank page.
2020-08-25 - Email Geeks
Marketer view
Marketer from Email Geeks says: Even if direct consumer domains are excluded, other domains like Windowslive.com, Dbmail.com, Dartybox.com, Netcabo.pt, or Webtv.net might still route through Microsoft's mail exchange servers.
