Summary
Microsoft utilizes two primary scoring systems, Spam Confidence Level (SCL) and Bulk Complaint Level (BCL), to assess incoming emails and determine their inbox placement. While both relate to an email's perceived quality, they measure different aspects of email traffic. Understanding these scores is crucial for maintaining strong email deliverability to Microsoft domains, including Outlook.com and Microsoft 365 (formerly Office 365). A high SCL suggests the message is likely spam, whereas a high BCL indicates the email is perceived as unwanted bulk mail, often due to recipient complaints or list quality issues, even if the content itself isn't overtly spammy.
Key findings
- SCL vs. BCL: SCL (Spam Confidence Level) is Microsoft's assessment of how likely an email is to be spam. BCL (Bulk Complaint Level) measures the likelihood that an email is part of a bulk mailing campaign that generates complaints. They are distinct indicators.
- Filtering impact: Both SCL and BCL scores influence whether an email lands in the inbox or the junk folder. Admins of Microsoft 365 environments can configure how different SCL and BCL thresholds are handled, affecting deliverability for their users.
- Complaint correlation: A high BCL, particularly for marketing or promotional emails, often signifies a high rate of recipient complaints, even for ostensibly legitimate, opted-in newsletters. This is a critical indicator that recipients find the mail undesirable.
- IP vs. domain reputation: While domain reputation is important, a high BCL score, especially when coupled with a clean domain reputation, can point to issues with the IP range being used. Shared IP ranges, if used by malicious or high-complaint senders, can negatively impact your BCL.
Key considerations
- Monitoring scores: Regularly monitor your SCL and BCL scores to understand how Microsoft perceives your email traffic. While direct score access isn't always available, analyzing email headers can provide insights (e.g., how to interpret SCL scores).
- Content and engagement: Even with an opted-in list, if your emails are not engaging or are perceived as irrelevant by recipients, they are more likely to mark them as junk, leading to higher BCLs. Reviewing email template changes and audience segmentation can help.
- List hygiene: A clean, engaged email list is paramount. High BCLs can often be traced back to outdated lists, unengaged subscribers, or poor consent practices, leading to higher complaint rates. Removing inactive subscribers can mitigate this.
- Shared IP ranges: If you are using shared IP ranges, their reputation directly impacts your deliverability. If other senders on the same IP are generating high complaints, your emails may suffer from a high BCL, even if your practices are clean. Microsoft's documentation on bulk complaint level values provides further detail.
What email marketers say
Email marketers often grapple with Microsoft's SCL and BCL scores, especially when facing inconsistent deliverability to Outlook and Microsoft 365 environments. Their experiences highlight the nuanced differences between spam detection and the categorization of unwanted bulk mail. Many find that even with perfectly opted-in lists, a high BCL can be a persistent challenge, often pointing to issues beyond traditional spam filters, such as recipient perception and the reputation of shared IP infrastructure. The struggle to differentiate between a truly spammy message (high SCL) and a legitimate bulk message that simply generates complaints (high BCL) is a common theme.
Key opinions
- Bulk vs. spam distinction: Marketers frequently distinguish between spam and bulk email, where bulk (or greymail) isn't necessarily malicious but is unwanted by recipients, leading to higher BCLs.
- Complaint-driven BCL: A high BCL is often directly tied to recipient complaints. Even if the content is not inherently spammy and the list is opted-in, consistent complaints will elevate this score.
- IP reputation influence: When domain reputation is strong, but a high BCL persists, marketers often suspect shared IP reputation as a root cause, particularly in B2B scenarios where Microsoft domains are prevalent.
- Admin configurability: The knowledge that O365 admins can customize their bulk mail filtering rules adds another layer of complexity for marketers, as their deliverability can be impacted by individual recipient organization settings.
Key considerations
- Audience segmentation: To mitigate high BCLs, marketers should focus on highly segmented and engaged lists, ensuring content relevance to reduce recipient complaints.
- Content relevance: Beyond explicit spam triggers, content that feels irrelevant or too frequent to recipients, even if opted-in, can lead to complaints and poor BCL scores. This aligns with broader efforts to improve email deliverability rates.
- Feedback loops: Actively participating in feedback loops (FBLs) with Microsoft is crucial. This helps identify and remove users who mark emails as spam, directly addressing the source of BCL issues.
- Sender requirements: Staying compliant with Microsoft's evolving sender requirements, including email authentication (SPF, DKIM, DMARC), is fundamental to establishing trust and avoiding deliverability penalties. Our guide on how to comply with Outlook's new sender requirements can provide further details.
Marketer view
Email marketer from Email Geeks suggests that SCL and BCL are tied to different indicators, with SCL relating to spam and BCL to bulk mail. The key difference is that bulk mail isn't necessarily unsolicited spam but can still generate complaints if recipients don't want it.
Marketer view
Marketer from Spotler explains that consistent junk or quarantine placement in Microsoft is often linked to high Spam Confidence Level (SCL) and Bulk Complaint Level (BCL) scores. These scores are key determinants of inbox placement.
What the experts say
Email deliverability experts provide critical insights into the distinction and interplay between Microsoft's SCL and BCL ratings. They clarify that SCL is a general spam confidence score, while BCL specifically targets bulk mail and its propensity to generate complaints. Experts emphasize that while both can lead to mail being junked, the underlying causes and remediation strategies often differ. They frequently highlight the configurable nature of BCL by O365 administrators and the direct correlation between recipient complaints and a high BCL, regardless of the sender's perceived legitimacy or list opt-in status. The consensus is that high scores in either category signal a need for detailed investigation into sending practices, content, and list engagement.
Key opinions
- SCL vs. BCL definitions: Experts confirm that SCL is the Spam Confidence Level and BCL is the Bulk Complaint Level (or bad bulk mail confidence level), clearly distinguishing between general spam and unwanted bulk email.
- Recipient-driven BCL: The primary driver for a high BCL is the mail you're sending causing complaints from recipients, regardless of whether they initially opted in.
- Admin control: A key difference is that BCL filtering can be directly customized by the O365 admin, allowing them to adjust sensitivity to bulk mail, whereas SCL filtering also has defaults but is broadly applied across consumer and hosted platforms.
- Interpreting mixed scores: If SCL is low (not spammy) but BCL is high (spammy for bulk), it means Microsoft isn't flagging the content as traditional spam, but the bulk nature of the mail is generating complaints.
Key considerations
- Focus on complaints: To improve BCL, the focus must be on reducing recipient complaints through better list management and content relevance, as detailed in our guide on how to improve my SCL on Outlook (which covers broader complaint issues).
- Holistic deliverability: Even with perfect authentication, high BCL or SCL issues indicate deeper problems. A holistic approach covering sending frequency, content, and list quality is required to fix Outlook junk mail placement.
- Shared IP risks: When using shared IPs, the reputation of other senders on that IP directly affects your BCL. If your domain reputation is good but your IP is questionable, this is a likely cause. This echoes the broader challenges of why Microsoft email deliverability issues are unusually bad.
- Confidence vs. complaint: While the 'CL' often means 'Confidence Level', in BCL, Microsoft specifically uses 'Complaint Level' to signify its direct link to user feedback. This nuance is critical for accurate diagnosis.
Expert view
Expert from Email Geeks confirms that SCL is the Spam Confidence Level, while BCL is specifically for 'bad' bulk mail confidence level, such as greymail, clarifying their distinct purposes.
Expert view
Expert from Word to the Wise emphasizes that a high BCL score signifies that the sender tends to cause complaints, indicating a problem with recipient engagement or content relevance for bulk mail.
What the documentation says
Official Microsoft documentation details the distinct roles of SCL and BCL in their anti-spam policies. It clearly defines SCL as a measure of an email's likelihood to be spam, considering various factors like content, sender reputation, and authentication. BCL, on the other hand, is specifically presented as the Bulk Complaint Level, directly reflecting the probability that an email is part of a bulk campaign that generates recipient complaints. The documentation also outlines the configurable nature of these scores by Microsoft 365 administrators, allowing organizations to fine-tune their filtering based on their specific needs and tolerance for bulk mail. This distinction is crucial for senders aiming to optimize their email deliverability to Microsoft environments.
Key findings
- Definitions: SCL stands for Spam Confidence Level, indicating the likelihood a message is spam. BCL stands for Bulk Complaint Level, assessing the probability an email is part of a bulk campaign that generates complaints. This is critical for understanding what factors influence a BCL 6 score.
- Junk vs. bulk: Microsoft differentiates between junk email (spam) and bulk email (greymail), with separate metrics (SCL and BCL) to categorize and filter them.
- Admin controls: Microsoft 365 anti-spam policies allow administrators to set actions based on SCL and BCL values, giving them control over how mail is handled (e.g., delivered to inbox, junk folder, quarantined). This configurability impacts how emails to Microsoft domains are throttled.
- Score ranges: SCL scores range from 0 (safest) to 9 (most spammy), while BCL scores range from 0 (least likely to generate complaints) to 9 (most likely to generate complaints).
Key considerations
- Message headers: SCL and BCL values are typically included in the email headers of messages processed by Microsoft Exchange Online Protection (EOP), allowing for diagnostic analysis.
- Sender reputation: Both SCL and BCL are heavily influenced by sender reputation, including IP and domain reputation, as well as the history of complaints generated by the sender's traffic. This connects to broader factors influencing email deliverability.
- Continuous adjustment: Microsoft's anti-spam algorithms, including SCL and BCL calculations, are continuously updated to adapt to evolving spam tactics, necessitating ongoing sender vigilance. For more technical insights, refer to the anti-spam policy documentation.
Technical article
Documentation from learn.microsoft.com explains that Bulk Complaint Level (BCL) values are utilized in Exchange Online Protection (EOP) to assess the likelihood of an email message being part of a bulk email campaign that generates user complaints.
Technical article
Documentation from University of South Dakota Knowledge Base states that Microsoft 365 uses both Spam Confidence Level (SCL) and Bulk Complaint Level (BCL) to rate incoming email messages, and these scores dictate how messages are handled by the anti-spam policy.
Related resources
9 resources
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