How can I monitor Microsoft reputation on a shared IP and what are third-party DKIM signatures?
Matthew Whittaker
Co-founder & CTO, Suped
Published 5 Jul 2025
Updated 19 Aug 2025
9 min read
Navigating email deliverability, especially with major providers like Microsoft, can be complex, particularly when operating on a shared IP address. Unlike dedicated IPs, shared IPs mean your sending reputation is tied to the practices of other senders using the same IP. This introduces challenges in monitoring and maintaining a good standing. Adding to this complexity are various email authentication mechanisms, including DKIM, and understanding what constitutes a 'third-party DKIM signature' is crucial for ensuring your emails reach the inbox.
Monitoring Microsoft reputation on a shared IP presents a unique set of hurdles. While Microsoft offers its Sender Score Data Network Services (SNDS), it primarily focuses on IP reputation and is limited for shared IP ranges and Office 365 hosted domains. This means you might not get detailed insights into your specific sending behavior on a shared IP. The challenge intensifies because a poor sender on your shared IP can negatively impact your own email deliverability, leading to legitimate emails landing in spam folders.
Many email professionals have observed a significant shift in how mailbox providers assess sender trustworthiness. There's a growing emphasis on domain reputation over solely relying on IP reputation. This shift means that while the shared IP still plays a role, your domain's sending history, authentication, and user engagement are becoming increasingly critical factors. This makes the job of monitoring Microsoft reputation more about understanding your domain's health than just the IP it's using.
The lack of granular IP-specific data for shared ranges within Microsoft's tools means you need to adopt alternative, more holistic strategies. Focusing on aggregate metrics and observing overall deliverability trends can provide more actionable insights. It’s also important to acknowledge that Microsoft (and other providers like Google) may be more prone to bulking emails from shared IPs if they detect any suspicious activity from the range, regardless of your individual sending quality.
To effectively manage your deliverability on a shared IP, it's essential to understand the limitations and then develop a proactive approach that leverages other data points. This typically involves a combination of email authentication, careful list management, and comprehensive monitoring beyond just IP reputation scores. For more insights on this, you can look at how sharing IP ranges affects deliverability.
Effective monitoring strategies
Since direct, granular IP reputation data for shared IPs with Microsoft is scarce, the best approach for monitoring involves focusing on metrics that reflect your domain's health and overall email performance. DMARC reports are invaluable for this, as they provide comprehensive feedback on SPF and DKIM authentication results, including details on where failures are occurring.
By analyzing DMARC reports, you can identify if your emails are passing authentication checks at Microsoft's receiving servers and, if not, why. This data can help you understand if Microsoft is marking your emails as spam due to authentication issues, which can indirectly reflect on the shared IP. You can find more about Microsoft email authentication on their official documentation.
Inbox placement testing using seed lists is another critical tool. Sending emails to a diverse set of mailboxes, including those from Microsoft domains, allows you to see exactly where your emails are landing: inbox, spam, or not delivered at all. This gives you a direct, real-world measure of your deliverability health with Microsoft, compensating for the lack of detailed IP reputation metrics. It also helps in observing if Microsoft is more likely to bulk your emails compared to other mailbox providers.
Lastly, paying close attention to engagement metrics (opens, clicks, unsubscribes, spam complaints) is vital. High engagement signals positive reputation, while low engagement and high complaint rates can quickly degrade it. These metrics, combined with Google Postmaster Tools for your sending domains, offer a comprehensive view that compensates for the limitations of shared IP monitoring tools for Microsoft reputation monitoring.
What are third-party DKIM signatures?
A third-party DKIM signature refers to a DKIM signature on your email that uses a domain other than your own. This typically happens when you send emails through a third-party service provider, like an Email Service Provider (ESP) or a transactional email platform. Instead of or in addition to your domain's DKIM signature, the service provider adds a DKIM signature using their own domain.
For example, if you use a platform like Google Workspace or SendGrid to send emails from yourdomain.com, and you haven't configured DKIM for yourdomain.com, the service might add a DKIM signature for something.gappsmtp.com or sendgrid.info. While this ensures the email is DKIM-signed, it's not signed by your domain.
The primary issue with third-party DKIM signatures is DMARC alignment. For DMARC to pass, either SPF or DKIM (or both) must align with the From domain shown to the recipient. If your email is only signed by a third-party DKIM domain, and not your own, it will fail DKIM alignment and potentially DMARC. This can severely impact deliverability, especially with strict receivers like Microsoft and Google and Yahoo.
Ideally, you always want your emails to be signed with your own domain's DKIM signature, regardless of whether you're using a third-party sender. This ensures proper DMARC alignment and strengthens your domain's reputation. Many reputable ESPs offer options for you to configure DKIM records for your domain, allowing them to sign emails on your behalf using your domain's private key.
Best practices for deliverability on shared IPs
While monitoring Microsoft reputation on a shared IP can be challenging, a strong focus on domain reputation and proper authentication is key. This means ensuring your SPF and DKIM records are correctly configured and that DMARC is implemented with a policy stronger than p=none. Regularly check your DMARC reports for any authentication failures, particularly those related to DKIM.
To effectively combat potential deliverability issues, consider these actions:
Configure DMARC: Move towards a p=quarantine or p=reject policy to ensure proper authentication and handling of unauthenticated emails. You can use our DMARC record examples.
Own DKIM Signature: Always ensure your emails carry your domain's DKIM signature, even when sending through a third-party. This is critical for DMARC alignment.
Monitor Engagement: Track open rates, click-through rates, and spam complaints across all mailbox providers, including Microsoft. This can provide early warnings of reputation issues.
Maintain Clean Lists: Regularly clean your email lists to remove inactive or invalid addresses, reducing bounces and spam trap hits.
By actively managing your domain's authentication and monitoring engagement, you can mitigate the risks associated with shared IP addresses and improve your overall email deliverability to Microsoft and other providers.
The path forward
For specific insights into your email security posture and to troubleshoot any authentication issues, Microsoft offers various security reports in their Defender portal. These reports, while not providing direct IP reputation for shared IPs, can still offer valuable data on email authentication results, spam detections, and other security incidents related to your domain. You can learn more about these email security reports.
The problem with shared IP monitoring
Limited Visibility: Microsoft's SNDS (Sender Score Data Network Services) offers general IP reputation, but not specific details for shared IP usage or how individual senders on that IP are performing. SNDS primarily monitors IP reputation.
Indirect Impact: A single bad actor on your shared IP can negatively impact your own deliverability, even if your sending practices are impeccable. This makes resolving IP reputation issues tricky.
No Domain-Level Data: Microsoft's tools generally don't provide domain-specific reputation data comparable to Google Postmaster Tools.
The transition in focus from IP reputation to domain reputation is a critical development in email deliverability. While shared IPs pose challenges, focusing on strong domain authentication (SPF, DKIM, DMARC) and consistent positive sending practices remains the most effective strategy. Always ensure your domain is properly authenticated, even when using third-party sending services, to maintain control over your sender reputation and improve deliverability to Microsoft and other mailbox providers.
Views from the trenches
Best practices
Actively use Google Postmaster Tools for domain reputation monitoring, even if it's primarily for Google, as reputation trends often correlate across major providers.
Implement DMARC with a enforcement policy like p=quarantine or p=reject to ensure strict authentication and gain valuable insight from aggregated reports.
Prioritize acquiring your own DKIM signature for all sending domains, especially when using third-party email service providers, to maintain full DMARC alignment.
Conduct regular seed list inbox placement tests to directly observe where your emails are landing across various mailbox providers, including Microsoft.
Maintain exceptional list hygiene by regularly cleaning inactive subscribers and removing bounces to minimize spam complaints and maintain a healthy sender reputation.
Common pitfalls
Relying solely on IP reputation tools like SenderScore, which provide limited data for shared IPs and often lack insights from major mailbox providers like Microsoft and Google.
Ignoring third-party DKIM signatures provided by ESPs without configuring your own domain's DKIM, leading to DMARC alignment failures and lower deliverability.
Neglecting to monitor DMARC reports, which contain crucial data on authentication failures that can indicate underlying deliverability issues with shared IPs or third-party senders.
Failing to adapt to the industry's shift towards prioritizing domain reputation over IP reputation, leading to misguided deliverability strategies.
Not actively monitoring engagement metrics (opens, clicks, complaints) per mailbox provider, missing early indicators of declining reputation.
Expert tips
If using a shared IP, actively manage your sending practices to be exemplary. This means high engagement, low complaints, and strict adherence to email authentication standards.
Work with your ESP to ensure they support custom DKIM signatures for your domain to maximize DMARC alignment and control over your sender identity.
For shared IPs, consider segmenting your audience and sending lower-risk, highly engaged emails from that IP to build a better reputation, while potentially using a dedicated IP for higher-volume or riskier sends.
Regularly review your email content for anything that might trigger spam filters, regardless of IP or domain reputation, as content plays a significant role in inbox placement.
Engage directly with Microsoft's support or communities if you encounter persistent deliverability issues, as they may offer specific guidance for unique situations.
Expert view
Expert from Email Geeks says they rely less on SenderScore now because domain reputation has largely taken over IP reputation in importance for deliverability.
2023-07-19 - Email Geeks
Marketer view
Marketer from Email Geeks says they measure domain reputation primarily through Google Postmaster Tools and inbox placement tests.
2023-07-19 - Email Geeks
Summary
Monitoring Microsoft reputation on a shared IP involves a strategic shift from solely relying on IP metrics to prioritizing domain reputation. While Microsoft's SNDS has its limitations for shared environments, robust email authentication through DKIM (especially ensuring your domain's own signature), along with SPF and DMARC, becomes paramount. Supplement this with continuous inbox placement testing and detailed engagement analytics. By focusing on these proactive measures, you can effectively manage your email deliverability and maintain a strong sender reputation, even when sharing an IP address.
