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

Summary

High BCL scores and junk folder placement are multifaceted, influenced by Microsoft's BCL scoring based on spam complaints, poor sender reputation, lack of email authentication (SPF, DKIM, DMARC), low engagement, spammy content, blacklisting, and sudden sending volume spikes. Addressing these involves warming new IPs/ESPs, ensuring wanted mail through opt-in, improving content quality and engagement, implementing authentication, managing sender reputation and monitoring metrics, and avoiding spam triggers and poor HTML. Crucially, understanding the BCL metric's Microsoft-specific context is important.

Key findings

  • Microsoft BCL Score: BCL is a Microsoft-specific score reflecting the likelihood an email is bulk, affecting Office365 filtering. Higher scores increase the chance of junking.
  • Sender Reputation is Paramount: Poor sender reputation, stemming from low engagement, high complaints, or blacklisting, is a leading cause of spam folder placement.
  • Email Authentication: Implementing SPF, DKIM, and DMARC is essential for verifying sender identity and improving deliverability.
  • Engagement Drives Placement: Low open and click rates negatively impact sender reputation, contributing to spam filtering.
  • Content Matters: Spammy content, trigger words, and poor HTML significantly increase the risk of emails being marked as spam.
  • List Hygiene is Key: Sending to unengaged users harms sender reputation. Opt-in practices and easy unsubscribe options are crucial.
  • Volume Spikes Trigger Filters: Sudden increases in sending volume, especially without warming up new IPs, can trigger spam filters.
  • Warm-up is Essential: New email streams, whether from a new address or ESP, require a ramp-up period to establish a positive sending reputation.

Key considerations

  • Implement Authentication (SPF, DKIM, DMARC): Verify your sending domain with properly configured SPF, DKIM, and DMARC records.
  • Create Engaging Content: Craft valuable and relevant content that encourages recipients to open, read, and click.
  • Maintain a Clean Email List: Regularly remove unengaged subscribers and ensure a clear opt-in process.
  • Monitor Sender Reputation: Track your sending reputation, IP address, and domain for blacklisting and related issues.
  • Warm Up New IPs and ESPs: Gradually increase sending volume when using new IP addresses or email service providers.
  • Focus on Wanted Mail: Ensure users have explicitly opted in to receive your emails.
  • Understand BCL's Scope: Remember that BCL scores are specific to Microsoft's filtering practices.
  • Monitor Metrics: Track metrics that influence sender reputation and engagement and ensure any issues are fixed quickly

What email marketers say
9Marketer opinions

Emails land in junk folders with high BCL scores primarily due to poor sender reputation, often stemming from factors like lack of email authentication (SPF, DKIM, DMARC), low engagement rates, high complaint rates, spammy content, blacklisting, and sudden increases in sending volume. Solutions involve improving sender reputation through consistent sending practices, authenticating emails, ensuring valuable and engaging content, cleaning mailing lists, monitoring sending metrics, avoiding spam trigger words and poor HTML, using opt-in lists, and checking/delisting from blacklists.

Key opinions

  • Sender Reputation: Poor sender reputation is the most common cause of emails landing in spam. Factors contributing to this include low engagement, high complaint rates, and blacklisting.
  • Authentication: Lack of proper email authentication (SPF, DKIM, DMARC) significantly increases the likelihood of emails being marked as spam.
  • Engagement: Low open and click rates negatively impact sender reputation and can lead to spam folder placement.
  • Content: Spammy content, including excessive use of trigger words, poor HTML coding, and large image sizes, can trigger spam filters.
  • List Hygiene: Sending emails to unengaged or uninterested subscribers increases complaint rates and harms sender reputation. Clean and well-maintained lists are essential.
  • Sending Volume: Sudden spikes in sending volume, especially without proper IP warming, can trigger spam filters.

Key considerations

  • Authentication Implementation: Ensure SPF, DKIM, and DMARC are properly configured and validated for your sending domain.
  • Engagement Optimization: Create valuable and engaging content that encourages recipients to open and interact with your emails.
  • List Management Practices: Regularly clean your email list by removing unengaged subscribers and implementing a clear opt-in process.
  • Sender Reputation Monitoring: Actively monitor your sender reputation, IP address, and domain using available tools and services.
  • Blacklist Monitoring and Removal: Check if your domain or IP is blacklisted and take steps to get delisted if necessary.
  • Sending Volume Strategy: Gradually increase sending volume over time, especially when using a new IP address or email service provider.
Marketer view

Email marketer from StackOverflow answers by suggesting creating a feedback loop as well as checking spamhaus. It's important to reach out to get delisted to prevent sending problems

October 2022 - StackOverflow
Marketer view

Email marketer from GlockApps explains that one key reason for emails going to spam folder is poor sender reputation. This can be caused by various factors, including low engagement, high complaint rates, or being listed on blacklists. They suggest monitoring your sending reputation, IP address, and domain using tools like theirs.

February 2025 - GlockApps
Marketer view

Email marketer from Mailjet shares that a high spam score (potentially contributing to high BCL and junking) can be caused by several factors, including poor sender reputation, lack of authentication (SPF, DKIM, DMARC), high complaint rates, spammy content, and blacklisting. They advise to authenticate your emails, monitor sender reputation, improve content quality, and manage your subscriber list.

October 2021 - Mailjet
Marketer view

Email marketer from Reddit shares that checking if your domain or IP is blacklisted is very important and can prevent emails going to spam. By cleaning the list or reducing sending you will have better engagement in the future.

June 2024 - Reddit
Marketer view

Email marketer from Sendinblue shares that factors influencing email deliverability and spam placement include sender reputation, authentication (SPF, DKIM, DMARC), engagement (open and click rates), and content. To improve deliverability, they recommend consistently sending valuable content, maintaining clean lists, and actively monitoring sending metrics to identify and address issues promptly.

December 2024 - Sendinblue
Marketer view

Email marketer from Litmus explains that consistent sending volume, proper authentication, and engaging content are crucial for good email deliverability. Sending frequency should be consistent, and you need to ensure SPF, DKIM, and DMARC are configured correctly. You also need to monitor your sender reputation to get ahead of deliverability problems.

February 2024 - Litmus
Marketer view

Email marketer from EmailonAcid shares that excessive use of spam trigger words, poor HTML coding, and large image sizes can contribute to emails being marked as spam. Make your emails mobile friendly and prevent use of suspicious code.

October 2022 - EmailonAcid
Marketer view

Email marketer from WarriorForum notes that sending unsolicited emails without permission will result in high spam scores and low deliverability. It is essential to use opt-in lists and segment leads

June 2023 - WarriorForum
Marketer view

Email marketer from Gmass explains that a low sender reputation will have emails marked as spam or not delivered. Improve engagement and authentications to fix sender reputation issues.

October 2024 - Gmass

What the experts say
8Expert opinions

High BCL scores and junk folder placement are influenced by several factors. The BCL score, assigned by Microsoft, reflects their confidence in whether an email is bulk, impacting filtering by Office365 customers. While DMARC alignment and custom return paths don't directly affect BCL scores, sending wanted mail, managing sending volume, and warming up new email streams are crucial. New or unwarmed sending streams and sudden volume spikes can trigger spam filters. Engagement is critical as low engagement can lead to emails landing in spam. Focusing on relevant content and ensuring clear opt-in processes and easy unsubscribe options can increase positive sender reputation.

Key opinions

  • BCL Scoring: BCL scores indicate Microsoft's confidence in an email being bulk, influencing filtering by Office365 customers. Higher scores increase the likelihood of junking, quarantining, or discarding.
  • Warm-up Requirements: New email streams, whether from a new address or ESP, require a warm-up period to avoid being flagged as spam.
  • Engagement Importance: Low email engagement (lack of opens/clicks) negatively impacts sender reputation and can lead to spam folder placement.
  • Content Relevance: Sending relevant and valuable content encourages recipient interaction and helps maintain a positive sender reputation.
  • Sending Volume Impact: Sudden spikes in sending volume without proper IP warming can trigger spam filters.
  • Opt-in/Unsubscribe Crucial: Obtaining clear opt-in and honoring unsubscribe requests are critical for ensuring emails are 'wanted' and avoiding spam complaints.

Key considerations

  • Sending Wanted Mail: Focus on sending mail only to users who have explicitly opted in, making it wanted rather than unwanted.
  • Content Strategy: Craft clear, honest, and easy-to-read content that is relevant and valuable to the recipient.
  • Gradual Volume Increase: Warm up new IP addresses and gradually increase sending volume to establish a positive sending reputation.
  • Monitor Engagement Metrics: Track open and click rates to identify and address potential deliverability issues.
  • List Segmentation: Segment your email list to send more targeted and relevant content to specific groups of subscribers.
  • Understand BCL: Understand that BCL is specific to Microsoft and affects filtering within Office365 environments.
Expert view

Expert from Email Geeks states that moving to a new ESP requires a warm-up period because it’s a different email stream.

November 2021 - Email Geeks
Expert view

Expert from Email Geeks explains that the BCL header is unrelated to DMARC alignment.

August 2021 - Email Geeks
Expert view

Expert from Word to the Wise explains that while landing in the promotions tab isn't necessarily bad, low engagement (lack of opens/clicks) can lead to spam folder placement. Focus on sending relevant and valuable content that encourages recipient interaction to maintain a positive sender reputation.

December 2021 - Word to the Wise
Expert view

Expert from Spam Resource shares that a sudden spike in sending volume without proper IP warming can trigger spam filters. Gradually increasing sending volume over time, and monitoring sender reputation, is critical for deliverability.

April 2021 - Spam Resource
Expert view

Expert from Email Geeks states that changing to a custom header in the return path will not change the BCL scoring.

November 2024 - Email Geeks
Expert view

Expert from Email Geeks explains that Outlook.com addresses don’t use BCL scores, but a new, unwarmed address is an underlying problem because Microsoft doesn’t like new mail streams.

May 2021 - Email Geeks
Expert view

Expert from Email Geeks shares that BCL is a score assigned by Microsoft, representing confidence in whether mail is bulk. Scores range from 0 (low confidence) to 9 (high confidence). BCL is primarily used in filtering by Office365 customers, who set their own thresholds for spam and choose actions like junking, quarantining, or discarding mail above that threshold.

August 2021 - Email Geeks
Expert view

Expert from Word to the Wise explains that avoiding spam filters requires focusing on sending wanted mail by obtaining clear opt-in, honoring unsubscribe requests, and segmenting lists. Content should be clear, honest, and easy to read. Technical setup and reputation are also crucial for reaching the inbox.

September 2021 - Word to the Wise

What the documentation says
4Technical articles

Emails are marked with high BCL scores and land in junk folders due to factors related to sender reputation, authentication, and bulk mail characteristics. Microsoft's Bulk Complaint Level (BCL) indicates the likelihood that a message is bulk mail based on spam complaints, with higher values suggesting a greater chance of generating complaints. Implementing SPF, DKIM, and DMARC authentication, managing sending reputation by minimizing bounces and complaints, and adhering to email content best practices can significantly improve deliverability and prevent emails from being marked as spam. DMARC is a critical defense to verify sender identity.

Key findings

  • BCL Interpretation: The Bulk Complaint Level (BCL) indicates the likelihood that a message is bulk mail based on spam complaints.
  • Authentication Importance: Implementing SPF, DKIM, and DMARC helps to verify sender identity and improve deliverability.
  • Reputation Management: Carefully managing sending reputation by keeping bounce and complaint rates low is critical for inbox placement.
  • Content Best Practices: Adhering to email content best practices helps to avoid triggering spam filters.

Key considerations

  • Implement SPF, DKIM, and DMARC: Configure SPF, DKIM, and DMARC records correctly to authenticate your sending domain and improve sender reputation.
  • Monitor and Manage Sending Reputation: Regularly monitor bounce and complaint rates, and take steps to address any issues promptly.
  • Optimize Email Content: Adhere to best practices for email content, such as avoiding spam trigger words and using appropriate formatting.
  • Dedicated IP Address: Consider using a dedicated IP address for sending email to better manage your sending reputation.
  • Implement DMARC: Implement DMARC to ensure that senders are who they say they are to prevent emails landing in Junk.
Technical article

Documentation from DMARC.org explains that implementing DMARC is a critical defense and the main way to prevent emails landing in junk. It is important to ensure that senders are who they say they are.

December 2022 - DMARC.org
Technical article

Documentation from Amazon AWS explains that using a dedicated IP address, authenticating your email with SPF, DKIM, and DMARC, carefully managing your sending reputation (keeping bounce and complaint rates low), and adhering to best practices for email content can significantly improve email deliverability and avoid junk folders. Also warm up your IP addresses.

December 2024 - Amazon AWS Documentation
Technical article

Documentation from RFC-Editor answers using the explanation of DKIM signatures. DKIM helps improve deliverability and reduces the chances of your email being marked as spam. Using DKIM and good email practices will prevent your emails from landing in junk folders

June 2024 - RFC-Editor
Technical article

Documentation from Microsoft Learn explains that the Bulk Complaint Level (BCL) indicates the likelihood that a message is bulk mail based on spam complaints. Higher BCL values indicate a greater probability that a message will generate complaints. Admins can configure anti-spam policies to filter messages based on BCL thresholds. Analyzing message headers for the 'X-MS-Exchange-Organization-BCL' property helps identify BCL scores.

April 2022 - Microsoft Learn