Summary
Microsoft email headers are crucial for deciphering why a message might be classified as spam. Headers like 'X-Forefront-Antispam-Report' and 'X-MS-Exchange-Organization-SCL' offer deep insights into Microsoft's spam filtering logic. They provide specific scores and verdicts related to spam likelihood, bulk mail perception, phishing attempts, and sender reputation, directly influencing how emails are processed and delivered. Analyzing these headers helps senders understand the factors contributing to deliverability outcomes.
Key findings
- SCL Score Impact: The 'X-MS-Exchange-Organization-SCL' header, providing the Spam Confidence Level (SCL), is a definitive indicator of an email's spam likelihood, with higher numerical values directly dictating actions like junking or quarantining.
- Detailed Verdicts: The 'X-Forefront-Antispam-Report' header offers granular diagnostics, including the 'SFV' (Spam Filter Verdict) which clearly states the immediate classification (e.g., 'SPM' for spam), and 'BCL' (Bulk Complaint Level) and 'PCL' (Phishing Confidence Level) that highlight perceptions of bulk or phishing activity.
- IP and Authentication Insights: Fields such as 'IPV' (IP Verdict) and 'PRV' (PTR Record Verdict) within the 'X-Forefront-Antispam-Report' reveal the sender's IP reputation and DNS configuration, while DMARC authentication results also significantly influence spam classification.
- Rule-Level Specificity: The 'SFS' (Spam Filter Score) field details specific anti-spam rules that were triggered, offering actionable intelligence on problematic content or sending practices that contributed to the overall SCL.
Key considerations
- Parsing Complexity: While rich in data, Microsoft headers can be complex to interpret manually; tools like the Microsoft Header Analyzer simplify this process.
- IP Reputation Priority: Microsoft's spam filtering heavily prioritizes IP address reputation, including that of nearby IPs, making it a critical factor for deliverability into Outlook.
- Policy Triggers: High SCL scores directly activate Microsoft's internal anti-spam policies within Exchange Online Protection (EOP), determining the message's final disposition, such as placement in the Junk Email folder or rejection.
- Proactive Adjustment: Understanding these header values enables senders to proactively identify and rectify issues related to content, sender reputation, or authentication that negatively impact their email deliverability.
What email marketers say
11 marketer opinions
Microsoft email headers, particularly 'X-Forefront-Antispam-Report' and 'X-MS-Exchange-Organization-SCL', provide a detailed roadmap for understanding their spam classification decisions. These headers offer granular insights into why an email might be flagged as spam, revealing specific scores, verdicts, and rules that were triggered. Analyzing these elements helps email marketers pinpoint issues related to content, sender reputation, or authentication, guiding necessary adjustments to improve deliverability.
Key opinions
- Core Header Insights: The 'X-Forefront-Antispam-Report' header serves as a primary source for detailed spam classification data, offering various sub-fields that explain Microsoft's assessment.
- Spam Filter Verdicts: The 'SFV' (Spam Filter Verdict) field within 'X-Forefront-Antispam-Report' provides a concise, immediate verdict, such as 'SPM' for spam, 'BLK' for blocked, or 'NLI' for non-spam, indicating the filter's direct assessment.
- Complaint & Phishing Levels: Values like 'BCL' (Bulk Complaint Level) and 'PCL' (Phishing Confidence Level) are critical indicators, signaling whether a mail is perceived as unsolicited bulk or a phishing attempt, both of which heavily influence its spam score.
- Triggered Rule Identification: The 'SFS' (Spam Filter Score) field enumerates specific anti-spam rules that were triggered, allowing senders to identify and correct problematic content or sending practices.
- Sender Reputation Checks: Fields such as 'IPV' (IP Verdict) and 'PRV' (PTR Record Verdict) reveal Microsoft's assessment of the sender's IP reputation and reverse DNS configuration, directly impacting the Spam Confidence Level (SCL).
- Authentication Impact: While not a direct spam score, DMARC authentication results, often indicated by fields like 'CompAuthResult', reveal if Microsoft successfully validated the sender's domain, with a 'pass' positively influencing spam classification and a 'fail' contributing to a higher SCL.
- Multi-Layered Scoring: The 'X-Microsoft-Antispam' header often contains internal spam IDs or scores, showcasing Microsoft's multi-layered approach to spam detection where various internal scores contribute to the final SCL.
Key considerations
- IP Address as Primary Cause: IP address issues are frequently the primary cause when emails are moved to the spam folder by Microsoft, highlighting the importance of a clean sending IP reputation.
- Leveraging Analyzer Tools: The complexity of parsing raw Microsoft headers makes tools like the Microsoft Header Analyzer invaluable for efficient interpretation and diagnosis.
- Interpreting Verdicts: A clear verdict like 'SFV:SPM' means the message was caught by a spam filter, requiring senders to investigate content or sending practices that triggered the mechanism.
- Addressing High Scores: High scores in BCL, PCL, or a failing IPV/PRV signify critical issues that will lead to stricter email handling, necessitating immediate action to rectify sending practices or infrastructure.
- DMARC Importance: Ensuring proper DMARC authentication is crucial, as a 'pass' strengthens trust signals and positively impacts deliverability, while a 'fail' can contribute to a higher spam score.
Marketer view
Marketer from Email Geeks shares links to Microsoft documentation about anti-spam headers, including BCL (Bulk Complaint Levels), PCL (Phishing Confidence Level), and SCL (Spam Confidence Level), and also provides a link to the Microsoft Header Analyzer tool for easier parsing.
23 Jan 2024 - Email Geeks
Marketer view
Marketer from Email Geeks suggests that IP address issues are often the primary cause when emails are moved to spam by Microsoft.
24 Jun 2022 - Email Geeks
What the experts say
4 expert opinions
Microsoft email headers, including X-Microsoft-Antispam and X-Forefront-Antispam-Report, are instrumental in understanding how Microsoft's spam filters evaluate messages. These headers reveal key data points like the Spam Filtering Verdict (SFV), Spam Confidence Level (SCL), Phishing Confidence Level (PCL), and IP Verdict (IPV). By analyzing these fields, senders gain crucial insight into whether an email was classified as clean, spam, or phishing, and the specific factors that contributed to its deliverability outcome. This detailed information allows email marketers to diagnose and address potential issues impacting their email placement.
Key opinions
- Comprehensive Evaluation Data: Microsoft headers, specifically X-Microsoft-Antispam and X-Forefront-Antispam-Report, detail how messages are evaluated by their spam filters, including verdicts and confidence levels.
- Key Diagnostic Fields: Essential fields like SFV (Spam Filtering Verdict), SCL (Spam Confidence Level), PCL (Phishing Confidence Level), CRL (Compromised Reputation Level), and IPV (IP Verdict) directly indicate classification and contributing factors.
- Insight into Classification Rationale: These header fields provide specific reasons for an email's disposition, whether it's delivered to the inbox or moved to the spam folder.
- IP Address's Critical Role: Microsoft's spam classification heavily depends on the reputation of the sender's IP address, extending to nearby IP addresses in the same network block.
Key considerations
- Diagnostic Value: Despite some expert views that SCL and BCL scores alone might not always fully explain why an email landed in spam, the comprehensive data within X-Microsoft-Antispam and X-Forefront-Antispam-Report headers is widely regarded as crucial for diagnosing deliverability problems.
- IP-Centric Filtering: Senders must recognize Microsoft's strong emphasis on IP address reputation, including the reputation of IP addresses in close proximity, as a primary driver for spam classification.
- Actionable Insights: The detailed verdicts and confidence levels provided by these headers empower senders to pinpoint specific issues-be it content, reputation, or infrastructure-that require corrective action.
Expert view
Expert from Email Geeks explains that Microsoft headers, including SCL and BCL scores, are not typically helpful for understanding why an email was moved to spam.
12 Mar 2023 - Email Geeks
Expert view
Expert from Email Geeks notes that Microsoft's spam filtering is heavily reliant on IP addresses, including nearby IP addresses.
4 Nov 2022 - Email Geeks
What the documentation says
3 technical articles
Microsoft email headers reveal comprehensive details about how their systems classify messages, especially concerning spam. Key headers, including 'X-Forefront-Antispam-Report' and 'X-MS-Exchange-Organization-SCL', provide a clear breakdown of an email's evaluation by Microsoft's anti-spam filters. These headers offer specific verdicts and confidence levels, such as the Spam Confidence Level (SCL) and Spam Filter Verdict (SFV), which directly determine whether an email reaches the inbox, junk folder, or is quarantined. Furthermore, they expose crucial reputation scores related to the sender's IP address, bulk mail perception, and phishing likelihood, all of which are central to Microsoft's precise spam classification process.
Key findings
- SCL as a Core Metric: The 'X-MS-Exchange-Organization-SCL' header provides the definitive Spam Confidence Level (SCL) score, which directly dictates how Microsoft Exchange or Exchange Online Protection (EOP) handles a message, from junking to quarantining or allowing it through.
- Detailed Spam Verdicts: The 'X-Forefront-Antispam-Report' header includes the 'SFV' (Spam Filter Verdict) field, explicitly indicating the classification outcome, such as 'SPM' for spam.
- Reputation and Content Indicators: Within 'X-Forefront-Antispam-Report', fields like 'BCL' (Bulk Complaint Level), 'PCL' (Phishing Confidence Level), 'IPV' (IP Verdict), and 'PRV' (PTR Record Verdict) offer critical insights into bulk mail perception, phishing risk, and the sender's IP and DNS reputation.
- Policy Enforcement: Microsoft's internal anti-spam policies within EOP directly utilize the SCL score to determine automated mail flow actions, ensuring consistent processing based on the message's calculated spam likelihood.
Key considerations
- Understanding SCL Thresholds: Senders must understand the SCL scoring range, typically -1 to 9, where higher scores directly lead to messages being junked or quarantined, while -1 indicates a message bypassed spam filtering.
- Holistic Header Analysis: A complete review of both 'X-Forefront-Antispam-Report' and 'X-MS-Exchange-Organization-SCL' headers is crucial for gaining a full understanding of the various factors contributing to Microsoft's spam classification.
- Direct Mail Flow Impact: The SCL score is not merely diagnostic; it directly dictates internal mail flow rules within Exchange Online Protection (EOP), underscoring its significant role in email deliverability.
- Reputation Signal Importance: Fields such as IPV and PRV within the headers emphasize Microsoft's strong reliance on the sender's IP and reverse DNS reputation as key contributors to the overall spam assessment.
Technical article
Documentation from Microsoft Learn explains that the 'X-Forefront-Antispam-Report' header contains key fields like 'SFV' (Spam Filter Verdict) which indicates the outcome (e.g., 'SPM' for spam), 'SCL' (Spam Confidence Level) which is a numerical rating of spam likelihood (0-9, higher means more spam), 'PCL' (Phishing Confidence Level), and 'BCL' (Bulk Complaint Level). Other fields like 'IPV' (IP Verdict) and 'PRV' (PTR Record Verdict) also contribute, revealing reputation aspects of the sender's IP and reverse DNS, all vital for Microsoft's spam classification.
23 Jun 2023 - Microsoft Learn
Technical article
Documentation from Microsoft Learn shares that the 'X-MS-Exchange-Organization-SCL' header provides the final Spam Confidence Level (SCL) score assigned to an email by Microsoft Exchange or Exchange Online Protection (EOP). This integer value, typically ranging from -1 to 9, directly informs downstream mail flow rules or policies on how to handle the message, such as routing it to the Junk Email folder (SCL 5, 6), quarantining it (SCL 7, 8, 9), or allowing it through (SCL 0, 1). A value of -1 indicates the message bypassed spam filtering.
27 Mar 2025 - Microsoft Learn
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