Why are my emails marked with a high BCL score and landing in junk folders, and how can I fix it?

Key findings

• BCL's role: A high BCL score (e.g., 4 or 6) indicates Microsoft's strong belief that an email is bulk, influencing its delivery to the junk folder. This score is distinct from DMARC alignment and is primarily used by Office 365 customers to filter mail based on their configured thresholds.
• Filtering decisions: Each Office 365 instance owner sets their own threshold for what BCL score causes an email to be junked, quarantined, or discarded. Thus, a score of 4 or 6 may be a deliberate decision by the recipient's system configuration.
• Impact of new mail streams: Microsoft tends to be cautious with new email streams or those that haven't been adequately warmed up, often sending them to spam or junk folders regardless of a low BCL score, as noted by some experts.
• Authentication vs. BCL: Proper SPF and DKIM setup is essential, but it does not directly prevent a high BCL score. The BCL score is a separate indicator of bulk mail likelihood. For more on improving Outlook deliverability, see our article on fixing Outlook junk mail placement.
• Custom return path: Changing to a custom domain in the return path (MAILFROM) may not directly impact BCL scoring, though it can aid SPF alignment.
• Email header analysis: Analyzing Exchange Online email headers can provide valuable insights into why a message was marked as junk or quarantined, including its BCL score.

Key considerations

• Content and engagement: Focus on email content quality and recipient engagement to improve sender reputation, as these factors heavily influence BCL and deliverability.
• Audience segmentation: Ensure you are sending relevant emails to engaged subscribers. High complaint rates can increase BCL scores.
• Warm-up process: If you are using a new sending IP or domain (even with an existing ESP), a proper warm-up strategy is crucial to establish a positive sending reputation with Microsoft and other ISPs.
• Monitoring deliverability: Continuously monitor your deliverability and BCL scores. While you cannot decode the X-Microsoft-Antispam-Message-Info header directly, tracking BCL trends helps. Consider our guidance on why emails land in Office 365 spam folders.

Key opinions

• Unexpected junking: Even with successful authentication, marketers observe emails landing in junk folders, sometimes with high BCL scores, indicating a deeper issue than just technical setup.
• Consistency matters: Marketers who have been sending emails for months without issue can suddenly experience deliverability problems, suggesting shifts in filtering algorithms or recipient behavior.
• Content and reputation: Spam filters grade emails based on various factors, including content, links, authentication, and overall sender reputation. For instance, email reputation and content are key components.
• Phishing flags: Some users report their emails being marked as 'probably phishing' by systems like Forefront, even if they are legitimate messages.
• Bulk email settings: Marketers need to understand how their emails are perceived as 'bulk' and if recipients' systems are configured to junk emails with certain BCL values. For tips on why cold emails might be struggling, check our guide on fixing cold emails going to spam.

Key considerations

• Monitor delivery: Regularly check where your emails are landing, not just if they are sent. Test sends to different mailbox providers are essential.
• Understand recipient settings: Be aware that Office 365 administrators can set their own BCL thresholds. This means a good BCL for one recipient might be junk for another.
• Review content: Even if your technical setup is correct, overly promotional language, suspicious links, or poor formatting can trigger spam filters. Our article on important product emails going to spam provides more context.
• Subscriber list hygiene: Regularly clean your email lists to remove inactive or disengaged subscribers, which can negatively impact your sender reputation and BCL score.

Key opinions

• BCL and DMARC: The BCL header is unrelated to DMARC alignment. While DMARC is vital for authentication, BCL is a separate assessment by Microsoft on how confident they are that mail is bulk.
• BCL scoring: BCL is a score from 0 (low confidence) to 9 (high confidence) assigned by Microsoft, indicating the likelihood that a message is unwanted bulk mail. This score is primarily used by Office 365 customers.
• Customer thresholds: Each Office 365 customer can set their own threshold for BCL. If a score like 4 or 6 lands an email in junk, it's a deliberate decision by that O365 instance's owner.
• New mail streams: Microsoft disfavors new or unwarmed-up mail streams. A sudden shift to an ESP or new sending patterns, even if the service was used before, can lead to junking, irrespective of BCL score.
• Return-path impact: Changing to a custom header in the return path does not affect BCL scoring.
• Beyond BCL: Even a BCL:0 score doesn't guarantee inbox delivery. Other factors can still lead to emails landing in spam folders, highlighting the multifaceted nature of deliverability. For more on this, read our expert guide to email deliverability.

Key considerations

• Sender reputation: Focus on building and maintaining a strong sender reputation, as this is a primary driver for BCL scores and overall deliverability. This includes consistent sending volume and low complaint rates.
• Email authentication: While BCL is separate, robust authentication (SPF, DKIM, and DMARC) is foundational for trust with mailbox providers. Learn more with our simple guide to DMARC, SPF, and DKIM.
• Consistent sending: Maintain consistent sending patterns. Sudden spikes in volume or changes in email content can trigger bulk classifications.
• Recipient engagement: High engagement (opens, clicks) and low complaint rates signal to ISPs that your mail is wanted, which positively influences reputation scores like BCL. Consider the impacts of SCL and BCL on Outlook and Gmail deliverability.

Key findings

• BCL definition: BCL is a score (0-9) that indicates how likely a message is considered bulk mail, which recipients might deem unwanted 'graymail'.
• SCL and BCL interaction: Outlook utilizes both Spam Confidence Level (SCL) and BCL scores to categorize emails and decide their inbox placement. High scores for either typically lead to junk or quarantine.
• Filtering configuration: Anti-spam policies in Office 365 allow administrators to set actions (e.g., move to junk folder) based on a message's BCL score, such as checking bulk email settings.
• Impact on deliverability: A high BCL score signifies why an email was classified as spam or bulk, as described by Microsoft's email header analysis.
• Protection settings: Microsoft Secure Score improvements often involve configuring spam protection settings, including ensuring that the BCL is set to move messages above a certain threshold to the junk email folder.

Key considerations

• Understand policies: Familiarize yourself with Microsoft's anti-spam policies and how BCL is calculated and applied to ensure compliance and optimal deliverability. Our guide on Outlook's new sender requirements may be helpful.
• Configure thresholds: If you manage an Office 365 environment, review and configure your custom anti-spam policy settings regarding BCL to ensure proper filtering for your users.
• Bulk mail practices: Even if mail is legitimate, if it's perceived as 'bulk' by Microsoft's algorithms, it can incur a high BCL. Adhering to best practices for sending bulk emails is crucial. For broader understanding, refer to an in-depth guide to email blocklists.
• Header analysis: Utilize tools or methods to analyze email headers, specifically the X-Microsoft-Antispam header, to identify the BCL score and other filtering verdicts (SFV value).