Summary
SCL scores for the same email can vary significantly across different O365 accounts due to the highly dynamic, multi-layered, and personalized nature of Microsoft's Exchange Online Protection (EOP) filtering system. This variability stems from factors such as individual user feedback and personalized Bayesian filtering, real-time sender reputation evaluations, continuously updated anti-spam algorithms, and unique tenant-level configurations. Additionally, the distributed cloud infrastructure and various stages of email processing contribute to subtle differences in how the same message is assessed for each recipient, leading to non-uniform SCL assignments.
Key findings
- Personalized User Filtering: O365 employs highly personalized filtering, where individual user actions, such as marking emails as spam or safe, and Bayesian filtering that learns from each user's inbox, can lead to different SCL scores for the same email sent to different recipients.
- Dynamic EOP Environment: SCL scores are assigned by Exchange Online Protection (EOP), a highly dynamic and real-time system. Factors like live sender reputation lookups, transient network conditions, continuous algorithm updates, and the precise timing of evaluation can cause minor discrepancies between recipients.
- Tenant-Specific Configurations: Organizational or tenant-level settings within O365, including customized anti-spam policies, specific phishing-related controls, or even the aggregated complaint feedback from employees within a company, can influence SCL scores uniquely for that tenant.
- Layered Filtering Process: EOP's email processing involves multiple stages and layers of filtering, including connection filtering, content analysis, and policy enforcement. Variations can arise if an email triggers a different path or rule for one recipient compared to another earlier in this complex process.
- Cloud Infrastructure Factors: As a distributed cloud service, O365 operates across numerous servers and regions. Slight differences in the specific server instance processing an email, cached reputation data, load balancing, or even minor network latency can contribute to subtle SCL score variations between recipients.
Key considerations
- Review Tenant Policies: O365 administrators should review their tenant-level and user-specific anti-spam policies, custom transport rules, or mail flow rules, as these can significantly influence SCL scores and explain variations.
- Monitor BCL/PCL Scores: Be aware that BCL (Bulk Complaint Level) or PCL (Phishing Confidence Level) scores are often used in threshold scoring within O365, which can automatically set an SCL to 9 regardless of other factors, leading to variations.
- Understand Adaptive Filtering: Recognize that Exchange Online Protection (EOP) uses an adaptive, learning-based system. SCLs are not static and can shift based on continuous threat intelligence updates, global feedback, and an organization's or individual user's historical interactions.
- Focus on Sender Reputation: While recipient-specific factors play a role, maintaining a strong sender reputation is paramount. O365 considers global sender reputation dynamically, and consistent positive engagement can mitigate SCL fluctuations.
What email marketers say
12 marketer opinions
The reason SCL scores can differ for identical emails across various O365 accounts lies in the complex, real-time, and highly contextual nature of Microsoft's Exchange Online Protection (EOP). Rather than a static evaluation, EOP dynamically assesses each message based on a constantly evolving threat landscape, individual recipient interactions, and specific organizational configurations. This adaptive process, coupled with the distributed architecture of the cloud environment, means that even slight temporal or processing path variations can lead to distinct SCL assignments.
Key opinions
- Real-time Adaptive Intelligence: EOP's SCL assignments are highly fluid, influenced by continuous updates to its threat intelligence, real-time sender reputation checks, and adaptive learning algorithms that constantly refine their assessment based on global and specific user feedback.
- Individual Recipient Context: Each O365 account has a unique history with senders and personalized interactions, like marking emails safe or junk, which influences how EOP's machine learning models assess incoming mail, leading to customized SCLs for the same message.
- Tenant and Administrative Controls: Organizational-level settings, custom transport rules, mail flow rules, and manual administrator overrides, including BCL-PCL thresholds that force an SCL of 9, can significantly alter the SCL assigned to emails within a specific O365 tenant.
- Cloud Infrastructure Nuances: The distributed nature of O365's cloud environment, including varying server instances, cached reputation data, minor network latency, and the timing of processing, can introduce subtle differences in SCL evaluations for identical emails.
Key considerations
- Understand EOP's Dynamic Behavior: Recognize that SCL scoring is not fixed; it's a real-time, adaptive process that incorporates evolving threat intelligence and sender reputation, meaning scores can fluctuate.
- Review Tenant and User-Specific Rules: O365 administrators should regularly audit their organization's custom transport rules, mail flow rules, and user-defined safe-blocked lists, as these settings can directly impact SCL assignments and explain variances.
- Monitor BCL and PCL Thresholds: Be aware that high BCL (Bulk Complaint Level) or PCL (Phishing Confidence Level) scores can trigger automatic SCL 9 assignments, overriding other factors and contributing to perceived score discrepancies.
- Prioritize Sender Reputation & Engagement: A consistent positive sender reputation, built through good list hygiene and high user engagement, helps mitigate SCL fluctuations by signaling trustworthiness to O365's adaptive filtering systems.
Marketer view
Email marketer from Email Geeks suggests checking BCL or PCL scores, which are used in threshold scoring to set SCL to 9, and notes that O365 administrators can manually identify characteristics and assign an SCL of 9.
21 Oct 2024 - Email Geeks
Marketer view
Email marketer from Email Geeks suggests that tenant-level settings within O365, such as additional phishing-related settings, might control filtering and influence SCL scores.
19 Jun 2024 - Email Geeks
What the experts say
3 expert opinions
SCL scores for identical emails often differ across O365 accounts primarily because Microsoft's Exchange Online Protection (EOP) incorporates highly personalized and adaptive filtering mechanisms. These systems learn from individual user behaviors, such as reporting spam, and fine-tune their evaluations based on Bayesian filtering unique to each inbox. Furthermore, the aggregate feedback and complaint patterns specific to an entire organization or tenant can influence the SCL rating for all its users, leading to company-specific variations.
Key opinions
- Tenant-Specific Complaints: Aggregate 'this is spam' complaints from employees within a specific O365 instance can increase the SCL for that entire company, indicating a tenant-level impact of user feedback on spam sensitivity.
- Individualized Bayesian Learning: Exchange Online Protection (EOP) employs Bayesian filtering that customizes and learns from each user's specific inbox, allowing identical emails to receive different SCL scores based on individual recipient history and preferences.
- User-Driven Filter Tuning: Large email providers, including those using O365 infrastructure like Outlook.com, intentionally use individual user input to fine-tune filtering for each distinct mailbox, explaining why the same message might deliver to one user but not another.
Key considerations
- Prioritize User Engagement: Actively encourage positive user engagement and provide clear unsubscribe options to reduce complaint rates, as these directly influence SCLs at both individual and organizational levels.
- Understand Personalized Filtering: Recognize that O365's SCL assignments are not universal; they are deeply influenced by each recipient's unique interaction history and the system's ongoing learning process for individual inboxes.
- Monitor Tenant-Level Feedback: Be aware that high complaint rates within a specific organization's O365 tenant can lead to higher SCL scores for all mail directed to that tenant, making it crucial to manage subscriber quality.
Expert view
Expert from Email Geeks explains that O365 SCL ratings can be company-specific, suggesting that if employees at one instance are more sensitive to mail and complain, the SCL may be higher for that company. She clarifies that these scores are calculated based on 'this is spam' complaints, which can be tenant-specific, rather than direct administrative settings.
3 Oct 2021 - Email Geeks
Expert view
Expert from Spam Resource explains that SCL scores for the same email can vary when sent to different O365 accounts because Exchange Online Protection (EOP) utilizes Bayesian filtering that learns and customizes its filtering for each individual user's inbox. This personalization means that even identical emails to different recipients within Office 365 can receive different SCL scores.
6 Jan 2023 - Spam Resource
What the documentation says
5 technical articles
SCL scores for the same email can differ across various O365 accounts because Microsoft's Exchange Online Protection (EOP) operates on dynamic, real-time evaluations and customized policy applications within a distributed cloud environment. This means that while core algorithms are consistent, the specific context of each recipient-their unique configurations, the precise moment of assessment by a particular server instance, and the evolving global threat intelligence-can lead to nuanced variations in the assigned spam confidence level.
Key findings
- Dynamic Real-Time Evaluation: EOP continuously assesses sender reputation and content against evolving threat intelligence. This real-time, dynamic nature means that the exact moment an email is processed or the specific reputation data available can subtly influence the SCL assigned to different recipients.
- Recipient-Specific Configurations: Variations in SCL can stem from individual recipient settings, such as their personal safe or blocked sender lists, or specific anti-spam policies uniquely applied to a user or group within an O365 tenant.
- Multi-Stage Filtering Paths: EOP processes emails through multiple stages, including connection filtering, spam filtering, and policy enforcement. The same email might traverse slightly different internal paths or trigger different rules for distinct recipients, leading to varied SCL outcomes.
- Distributed Cloud Architecture: As a large-scale, distributed cloud service, O365's underlying infrastructure involves load balancing, regional differences, and dynamic resource allocation. These operational aspects can result in an email being evaluated in a slightly different computational context for each recipient, contributing to SCL score variations.
Key considerations
- Acknowledge EOP's Complexity: Understand that SCL assignment is not a simple, static process but a multi-layered, dynamic evaluation influenced by a multitude of real-time factors and evolving intelligence.
- Review Policy Customizations: Regularly check and manage customized anti-spam policies, safe-blocked sender lists, and other recipient-specific configurations within O365, as these directly impact SCL outcomes.
- Impact of Real-time Reputation: Recognize that sender reputation is continuously evaluated. Minor, real-time shifts in reputation or evaluation timing can cause subtle SCL differences, even for identical emails.
- Consider Infrastructure Nuances: Be aware that the distributed nature of O365's cloud environment can introduce slight variations in how emails are processed, leading to non-uniform SCL assignments across accounts.
Technical article
Documentation from Microsoft Learn explains that SCL scores are assigned based on multiple layers of filtering and reputation checks within Exchange Online Protection (EOP). While the core SCL algorithm is consistent, variations can occur due to dynamic, real-time evaluations of sender reputation, recipient-specific configurations (like individual safe/blocked sender lists, or custom anti-spam policies applied to specific users), and the evolving threat landscape, leading to slight differences even for the same email.
10 Mar 2022 - Microsoft Learn
Technical article
Documentation from Microsoft Learn indicates that anti-spam policies, which influence SCL, can be customized and applied to specific users, groups, or domains. This means if different O365 accounts are subject to different anti-spam policies or rules (e.g., default policy vs. a strict custom policy for certain users or groups), the same email could receive varying SCL scores due to these individualized policy applications.
29 Jan 2025 - Microsoft Learn
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