Summary
Even with proper authentication and the absence of public blacklist issues, Microsoft Defender may still classify one-to-one emails as spam with a high SCL score (9). This is due to multiple factors including content triggers, sender reputation (IP and domain history), recipient engagement, shared hosting impact, sending patterns, and overall infrastructure health. Microsoft's filtering extends beyond authentication, considering internal reputation lists and advanced content analysis. SNDS helps monitor IP health. Investigation into content triggers, sending patterns, and recipient interaction may be necessary to determine the root cause. Warm up processes can assist.
Key findings
- High SCL Implies Spam: An SCL of 9 is a strong indicator of spam and requires thorough investigation.
- Authentication Isn't Enough: Microsoft's spam filtering considers more than just authentication; content, engagement, and reputation are critical.
- Content Sensitivity: Microsoft Defender performs advanced content analysis. Avoid spam trigger words, URL shorteners, and excessive tracking pixels.
- Reputation Matters: Sender reputation is a significant factor. Use SNDS to monitor your IPs and resolve deliverability issues.
- Engagement Matters: Engagement (opens, clicks) influences sender reputation. Focus on delivering relevant content and encouraging interaction.
- Shared Hosting Risks: Shared hosting impacts IP reputation due to the activities of other users on the same server; a dedicated IP is preferable.
Key considerations
- Detailed Investigation: Share details about identity, business model, sending mechanics, and address acquisition to diagnose the issue.
- Content A/B Testing: A/B test different subject lines and body content to identify spam triggers.
- SNDS Monitoring: Monitor SNDS regularly for complaints and spam trap hits.
- Implement Feedback Loops: Use feedback loops to remove subscribers who mark emails as spam.
- List Hygiene: Regularly clean your email list to remove invalid addresses.
- Dedicated IP: Consider using a dedicated IP address to improve control over sender reputation.
- Engagement Optimization: Improve recipient engagement by sending relevant content.
- Consider URL Reputation: If your URLs are new or not widely used, Microsoft may consider them suspicious.
What email marketers say
12 marketer opinions
Despite proper email authentication (SPF, DKIM, DMARC) and the absence of blacklist issues, Microsoft Defender may still mark one-to-one emails as spam due to several factors. These include content-related triggers, sender reputation (IP and domain history), recipient engagement, the use of shared hosting, and incomplete isolation of activity. Content filters may be triggered by specific keywords, URL shorteners, or tracking pixels. Sender reputation is influenced by sending volume consistency, and feedback from recipients marking emails as spam. Recipient engagement (opens, clicks) significantly affects sender reputation with Microsoft. Also, the sending domain should only be used for the described activity.
Key opinions
- Content Matters: Even with proper authentication, email content can trigger spam filters. Test different subjects and content, avoid spam trigger words, URL shorteners, and excessive tracking pixels.
- Sender Reputation: Sender reputation, based on IP/domain history, sending volume, and recipient feedback, strongly impacts deliverability with Microsoft. Monitor SNDS and other reputation tools.
- Engagement is Key: Lack of positive engagement (opens, clicks) negatively affects sender reputation. Send relevant content and encourage interaction.
- Dedicated IP Recommended: If using shared hosting, the IP's reputation can be impacted by other users. Consider using a dedicated IP.
- Segment your sending: Ensure that all activity on the domain is trusted and expected, and only relates to the one-to-one email activity you are planning to do.
Key considerations
- Content Testing: A/B test different subject lines and body content to identify triggers for spam filters.
- Reputation Monitoring: Regularly monitor sender reputation using Microsoft SNDS and other tools.
- Feedback Loop Implementation: Implement a feedback loop to identify and remove subscribers who mark emails as spam.
- Engagement Optimization: Improve recipient engagement by sending relevant content and encouraging interaction.
- List Hygiene: Regularly clean your email list to remove inactive or invalid addresses.
- Consider Dedicated IP: Evaluate the benefits of moving to a dedicated IP address to improve control over sender reputation.
- Complete Isolation: Ensure that the domain is only being used for one-to-one email activity, if other activity is occurring that may impact reputation.
Marketer view
Email marketer from Reddit shares that even with perfect setup, Microsoft's algorithms are sensitive to content and engagement. He suggests A/B testing different subject lines and body content, and also ensuring recipients are actively engaging with the emails (not just ignoring or deleting them).
18 Aug 2023 - Reddit
Marketer view
Marketer from Email Geeks suggests trying different subject lines, friendly from addresses, removing external domains from the message, and removing the body content by dichotomy to identify the cause of the high SCL score.
18 May 2024 - Email Geeks
What the experts say
3 expert opinions
Despite correct authentication, Microsoft Defender marks one-to-one emails as spam likely due to content, sending patterns, recipient interaction, or infrastructure issues. An SCL of 9 suggests a high probability of spam, so it may require careful investigation. Sharing details about business model, sending mechanics, and content may help identify the cause.
Key opinions
- High SCL Score: An SCL of 9 strongly indicates spam, suggesting the issue is likely not a simple false positive.
- Authentication Isn't Enough: Microsoft's filtering goes beyond authentication; content, sending infrastructure, and recipient interaction are key.
- Content Triggers: Specific content elements (URL reputation, keywords) can trigger spam filters.
Key considerations
- Share Details: Provide comprehensive information about your identity, business model, and sending practices to facilitate troubleshooting.
- Investigate Content: Carefully examine email content for potential spam triggers and problematic URLs.
- Analyze Sending Patterns: Review sending patterns and infrastructure to identify any unusual or problematic behavior.
- Assess Recipient Interaction: Evaluate recipient engagement and identify any issues related to address acquisition or email relevance.
Expert view
Expert from Email Geeks explains that an SCL of 9 indicates a high probability of spam and suggests the issue is likely not a false positive. He suggests sharing more details about the identity, business model, sending mechanics, address acquisition, mail content, and other senders from the domain to speculate on the cause.
25 Jun 2022 - Email Geeks
Expert view
Expert from Word to the Wise explains that Microsoft's junk mail filter is affected by more than just authentication. The content, sending infrastructure, and recipient engagement also play a role. It may be necessary to perform more investigation to see if the content or sending behavior is out of line.
3 Sep 2021 - Word to the Wise
What the documentation says
3 technical articles
Microsoft Defender assigns Spam Confidence Levels (SCL) via Exchange Online Protection (EOP), with higher values indicating a greater likelihood of spam. An SCL of 9 signifies near certainty. Even without public blacklist appearances, Microsoft utilizes internal and external reputation lists to identify spamming source IPs. The Smart Network Data Services (SNDS) program provides a mechanism for senders to monitor their IP health and reputation within the Microsoft network.
Key findings
- SCL Meaning: SCL values from 0-9 indicate the probability that an email is spam.
- Reputation Matters: Microsoft maintains internal reputation lists, affecting deliverability regardless of public blocklists.
- SNDS Tool: SNDS allows senders to monitor their IP reputation and detect spam-related issues.
Key considerations
- Monitor SNDS: Regularly monitor your IPs in SNDS for complaint rates and spam trap hits.
- Improve IP Reputation: Address any issues identified in SNDS to improve your IP's reputation with Microsoft.
- Investigate SCL of 9: If receiving an SCL of 9, conduct a thorough investigation into potential causes, even with proper authentication.
Technical article
Documentation from Microsoft explains the Smart Network Data Services (SNDS) program allows senders to monitor the health and reputation of their sending IPs on the Microsoft network. This provides visibility into complaint rates and spam trap hits, which can help diagnose deliverability issues.
31 Jul 2021 - Microsoft SNDS
Technical article
Documentation from Microsoft clarifies that Microsoft uses internal and external reputation lists to identify source IPs that may be sending spam. Poor IP reputation, even if not on public blocklists, can cause messages to be flagged as spam.
15 Aug 2023 - Microsoft Learn
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