Summary
Many email senders find it confusing when Microsoft SNDS (Smart Network Data Services) shows a healthy reputation status (green light) for their sending IPs, yet their transactional emails are still experiencing deliverability issues at Microsoft domains. This often manifests as high bounce rates or emails landing in junk folders. The core of this discrepancy lies in how Microsoft handles different types of email traffic and the specific tools it uses to manage reputation for its various services.
Key findings
- SNDS limitation: SNDS data primarily pertains to Outlook.com and Hotmail.com consumer domains, not Office 365 (O365) business or corporate accounts. Therefore, a green status in SNDS doesn't guarantee good deliverability to O365.
- Bounce messages: Transactional email issues often appear as bounces with specific error codes, such as `5.7.606 Access denied, banned sending IP`, indicating a block by Microsoft's internal systems for O365 traffic.
- Separate reputation: Microsoft maintains distinct reputation systems for its consumer and business email services. Positive SNDS data for consumer mail does not necessarily reflect the sender's standing for business-to-business or transactional emails to O365.
- Internal blocklists: Issues with O365 frequently stem from an internal Microsoft blacklist or blocklist that is not visible via SNDS. Senders need to use the Office 365 Anti-Spam IP Delist Portal for removal requests.
- Complaint feedback: Unlike consumer domains, reputation for O365 domains is heavily influenced by end-user spam complaints (via the this-is-spam button), and this feedback is not relayed through SNDS or JMRP for O365 accounts.
Key considerations
- Delisting process: Regularly monitor bounce messages for Microsoft-specific error codes and use the designated delisting tool to request IP removal. Be aware that this might be a recurring task if underlying issues persist.
- Audience management: Implement robust data sanitization and list hygiene practices for transactional lists. Ensure that new contacts are genuinely engaged and expecting your emails, especially for business recipients (to reduce spam complaints).
- Supplier communication: If using a third-party sending platform (like Mailgun or Iterable), engage with their support team to understand if the IPs are shared and what measures they are taking to maintain reputation with Microsoft's O365 systems.
- Dedicated IP considerations: For high-volume transactional senders, consider using dedicated IPs to isolate your sending reputation from other senders on shared IPs, allowing for more direct control over your standing with Microsoft.
- Proactive monitoring: Beyond SNDS, monitor bounce rates and complaint metrics specific to Microsoft domains to catch issues early, even if they aren't visible in SNDS.
What email marketers say
Email marketers often face a perplexing situation when their transactional emails fail to reach Microsoft inboxes, despite receiving positive indicators from SNDS. Their experiences highlight the nuanced nature of Microsoft's email filtering, particularly concerning its enterprise-grade Office 365 service versus its consumer-facing Outlook.com and Hotmail.com platforms. The common theme is a disconnect between the data provided by official tools like SNDS and the actual real-world delivery performance, especially for critical transactional messages.
Key opinions
- SNDS irrelevance: Many marketers quickly discover that SNDS data is not applicable to Office 365 deliverability, making it an unreliable indicator for transactional emails targeting business domains.
- Bounce codes matter: Specific bounce messages, like the `5.7.606 Access denied` code, are crucial clues, directly pointing to Microsoft's internal blocklists impacting O365 deliveries.
- Delisting challenges: The process of delisting IPs via the Office 365 portal is often slow and doesn't provide long-term solutions if the underlying reputation issues persist.
- Migration impact: Migrating to new sending platforms or IPs can significantly impact deliverability to Microsoft, even if prior performance was good, highlighting the sensitivity of their filtering systems.
- Acquisition process is key: Marketers frequently point to the address acquisition process and how recipients are added to lists as primary drivers of Microsoft deliverability, especially due to direct user spam complaints.
Key considerations
- Proactive delisting: Marketers should be prepared for ongoing delisting requests through the Microsoft IP Delist Portal when encountering `Access denied` bounces.
- Opt-in validation: Even for transactional emails (e.g., account invites), ensuring a robust opt-in or user-initiated process is critical to mitigate spam complaints and improve deliverability to Microsoft business accounts.
- Provider collaboration: Work closely with your email service provider (ESP) or Mail Transfer Agent (MTA) to understand the shared IP environment and to troubleshoot Microsoft-specific blocks, particularly if you've recently changed providers.
- Internal whitelisting efforts: While not a scalable solution, asking corporate recipients to whitelist your sending addresses can provide temporary relief and confirm that the issue is not at their end.
- Beyond SNDS monitoring: Marketers need to look beyond SNDS and focus on direct feedback loops (where available), bounce logs, and internal metrics (like open rates on O365 domains) to gauge true deliverability. Also check your domain reputation more broadly.
Marketer view
Marketer from Email Geeks explains that they are experiencing transactional deliverability issues specifically on the Microsoft side. They note that this is happening despite SNDS showing a green light for both of their IPs. The issue seems to be more prevalent with business and corporate domains.They are asking affected recipients to whitelist their addresses as a temporary measure, but are seeking other long-term solutions from the community.
Marketer view
Marketer from Spiceworks Community highlights that their emails, including those going to other Microsoft tenants and replies back to their own tenant, were encountering false positives from Defender ATP, ZAP, and Safelinks. This indicates that Microsoft's advanced threat protection features can sometimes incorrectly flag legitimate emails.These false positives can significantly disrupt transactional email flow, even if the sender's general reputation appears good on basic monitoring tools. It underscores the complexity of deliverability within Microsoft's ecosystem.
What the experts say
Email deliverability experts consistently point out that Microsoft's email ecosystem is complex, with different filtering mechanisms for its consumer (Outlook.com, Hotmail.com) and enterprise (Office 365) services. They emphasize that SNDS is largely irrelevant for O365 deliverability, which operates on its own set of reputation metrics, heavily influenced by user feedback that is not easily accessible to senders. Solutions often involve direct engagement with Microsoft's specific delisting tools and rigorous attention to list quality.
Key opinions
- SNDS vs. O365: Experts firmly assert that SNDS data has no bearing on Office 365 deliverability, as it pertains to different sets of accounts and internal reputation systems.
- User complaint impact: The this-is-spam button for O365 users directly impacts sender reputation at Microsoft, even if senders don't receive explicit feedback.
- Reputation management differences: Managing reputation for O365 requires a different approach than for consumer domains, focusing on minimizing internal complaints and maintaining extremely clean lists.
- Data sanitization critical: The quality of email addresses at the point of collection or addition is paramount, as bad data can lead to immediate and severe deliverability issues on O365.
- Shared IP risks: Using shared IPs, especially for transactional mail, means your deliverability can be impacted by the sending practices of other users, necessitating close communication with your ESP.
Key considerations
- Understand Microsoft's internal blocks: Recognize that O365 filtering relies on internal systems and not just public blacklists. Focus on resolving direct `Access denied` bounces through Microsoft's dedicated IP delisting portal.
- Strengthen acquisition practices: Even for internal-facing transactional emails, ensure the email addresses are valid and the recipients genuinely expect the communication. This can involve confirmation steps or clear user-initiated additions.
- Monitor real-time metrics: Rely on bounce rates, complaint metrics (if available via JMRP, though limited for O365), and engagement data rather than solely on SNDS for O365 deliverability. Consider how to boost email deliverability rates across all platforms.
- Content quality: Even for transactional emails, ensure content is clean, relevant, and avoids anything that could trigger spam filters. Review common issues that cause emails to go to spam.
- Authentication: Ensure your SPF, DKIM, and DMARC records are correctly configured and aligned, as these are foundational for Microsoft's filtering, especially for O365.
Expert view
Expert from Email Geeks clarifies that the bounce messages indicating `5.7.606 Access denied` are related to Office 365, and SNDS data is irrelevant for these issues. They emphasize that SNDS provides data only for consumer Outlook.com accounts, not for corporate O365 environments.This distinction is critical for senders to understand where to focus their troubleshooting efforts, as relying on SNDS for O365 problems will lead to misdiagnosis.
Expert view
Expert from Word to the Wise frequently advises that Microsoft's various mail properties (Outlook.com, Hotmail, Exchange Online/Office 365) operate with somewhat distinct reputation systems. A good reputation with one doesn't always translate directly to another, particularly between the consumer and enterprise platforms.This means a sender could have excellent standing on Outlook.com but face significant issues with a specific O365 tenant, depending on factors like local blocklists or user complaints within that organization.
What the documentation says
Official documentation and reliable deliverability guides provide crucial insights into Microsoft's email filtering mechanisms. These sources clarify the distinction between Microsoft's consumer and business email platforms and outline the official channels for addressing deliverability issues, particularly for IP blocks. They also emphasize the importance of standard email authentication protocols and good sending practices for maintaining a positive sender reputation with Microsoft.
Key findings
- SNDS scope: Microsoft's documentation for SNDS specifies that it provides data for Outlook.com and Hotmail.com, not necessarily for Office 365 (Microsoft 365) enterprise domains.
- Office 365 delisting: The dedicated Office 365 Anti-Spam IP Delist Portal is the official channel for requesting removal of an IP from Microsoft's internal blocklists that affect O365 deliveries, often triggered by `5.7.606` bounces.
- Authentication importance: Microsoft's guidelines strongly recommend implementing SPF, DKIM, and DMARC for all senders to establish sender authenticity and improve deliverability, especially to O365.
- JMRP limitations: While JMRP provides feedback on consumer complaints, its utility for O365 deliverability issues is limited as it may not capture feedback from corporate users.
Key considerations
- Monitor bounce codes: Pay close attention to specific SMTP bounce codes from Microsoft, as they provide direct instructions on how to proceed with delisting requests (e.g., the `5.7.606` error with a link to the delisting portal).
- Adhere to best practices: Microsoft's general sender guidelines emphasize building a good reputation through valid sending practices, including maintaining clean lists, sending wanted mail, and avoiding spam traps. This also includes addressing SPF DNS timeout issues specifically for Microsoft.
- Sender compliance: Microsoft continually updates its sender requirements, especially for bulk senders. Stay informed on how to comply with Outlook's new sender requirements which often impact transactional mail too.
- Feedback loops (FBLs): While limited for O365, participating in JMRP for consumer Outlook.com can provide insights into user complaints, which may indirectly reflect on overall sender reputation across Microsoft's ecosystem.
Technical article
Documentation from Microsoft's email deliverability guidance states that the `5.7.606 Access denied` bounce message indicates that the sending IP address is banned due to suspicious activity. It directs senders to a specific portal for requesting removal from this internal blocklist.This clearly indicates that such blocks are distinct from general public blocklists and require a direct interaction with Microsoft's own delisting tool, specifically `sender.office.com`.
Technical article
Documentation from the SendLayer blog outlines key strategies to improve deliverability to Outlook email addresses. It lists proper configuration of SPF, DKIM, and DMARC as fundamental requirements, alongside leveraging SNDS and JMRP (Junk Mail Reporting Program).The article also emphasizes smart sender practices, which typically include maintaining a clean list, sending relevant content, and ensuring a low complaint rate.
Related resources
4 resources
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