Summary
The 'MailBlockKnownSpammer' bounce indicates the receiving mail server perceives the sending IP or domain as a source of spam, primarily due to poor sender reputation. This can arise from multiple factors, including spam complaints, high bounce rates, suspicious sending patterns, being listed on blocklists (RBLs), sudden volume spikes, or even the content of the emails triggering spam filters. Resolving this involves a multi-faceted approach: immediately checking blocklist status and contacting the blocking entity (ISP or email provider) for remediation; verifying and improving sender reputation using tools and adhering to best practices; implementing proper email authentication (SPF, DKIM, DMARC); maintaining a clean email list and segmenting it for targeted sending; separating transactional and marketing emails to different IPs; gradually warming up new IPs; monitoring feedback loops and promptly addressing complaints; avoiding spam trigger words; and ensuring clear communication with recipients about the value of the messages. Reviewing SMTP logs can also reveal specific reasons for rejections.
Key findings
- Reputation is Paramount: Poor sender reputation is the primary cause of 'MailBlockKnownSpammer' bounces.
- Authentication is Essential: Proper email authentication (SPF, DKIM, DMARC) is crucial to verify sender identity and prevent spoofing.
- List Hygiene Matters: Maintaining a clean and engaged email list reduces bounce rates and spam complaints.
- Content Impacts Deliverability: The content of the email, including the use of spam trigger words, can affect deliverability.
- Monitoring is Key: Regularly monitoring IP and domain reputation is essential for proactive problem-solving.
- Segment Your Traffic: Separating transactional and marketing email IPs is essential to prevent reputation issues with critical traffic.
Key considerations
- Check Blocklists Immediately: Immediately check your IP and domain against common blocklists (RBLs) to identify potential issues.
- Contact Blocking Entities: Contact the blocking ISP or email provider to request delisting and demonstrate adherence to best practices.
- Implement Authentication Protocols: Configure SPF, DKIM, and DMARC records to authenticate your emails and improve deliverability.
- Clean Your Email List Regularly: Remove inactive, invalid, or unengaged subscribers from your email list to improve engagement rates.
- Segment Your Email Campaigns: Segment your email list based on engagement and demographics to send more targeted and relevant messages.
- Avoid Spam Trigger Words: Review your email content to avoid using spam trigger words or phrases that can flag your messages as spam.
- Monitor Your Reputation: Use tools like Google Postmaster Tools and Sender Score to monitor your IP and domain reputation.
- Monitor Engagement: Closely monitor user engagement metrics like opens, clicks, and spam complaints to identify and address potential deliverability issues.
- IP Warm-Up: Slowly warm up your IP address by gradually increasing sending volume when using a new IP address.
- Review SMTP Logs: Review your email server logs for specific SMTP error codes related to rejections.
- Use a Dedicated IP Address: Use a dedicated IP for transactional emails to protect its reputation.
What email marketers say
11 marketer opinions
The 'MailBlockKnownSpammer' bounce message indicates that the receiving mail server considers the sending IP or domain to have a history of sending spam. This can stem from various factors including poor sending practices, low engagement, spam complaints, being listed on blocklists (RBLs), or sudden increases in email volume. Resolution involves checking and improving sender reputation, ensuring proper email authentication (SPF, DKIM, DMARC), maintaining a clean email list, segmenting lists for targeted sending, separating transactional and marketing emails, warming up new IPs, monitoring feedback loops, and avoiding spam trigger words in email content. Contacting the recipient's email provider or security filter provider for delisting may also be necessary.
Key opinions
- Reputation: The primary cause is poor sender reputation due to perceived spam activity by the receiving server.
- Authentication: Lack of proper email authentication (SPF, DKIM, DMARC) can lead to deliverability issues.
- List Hygiene: Poor list hygiene, including inactive or invalid addresses, contributes to deliverability problems.
- Volume Spikes: Sudden increases in email volume, especially from new IPs, can trigger spam filters.
- Content: Spam trigger words or aggressive promotional language can flag emails as spam.
- Separation of traffic: Sending marketing emails via the same IP can negatively impact the reputation of critical transactional traffic.
Key considerations
- Monitor Reputation: Regularly check IP and domain reputation using tools like Sender Score and Google Postmaster Tools.
- Implement Authentication: Ensure SPF, DKIM, and DMARC are correctly configured to verify sender identity.
- Clean Email List: Remove inactive or invalid addresses from the email list to improve engagement rates.
- Segmentation: Segment the email list and send more targeted emails to improve engagement and relevance.
- IP Warm-up: Gradually increase email volume when using a new IP address to establish a positive sending reputation.
- Content Review: Avoid using spam trigger words and aggressive promotional language in email content.
- Feedback Loops: Monitor feedback loops and address complaints promptly to maintain a good sender reputation.
- Delisting: Contact the recipient's email provider or security filter provider for delisting if the IP or domain is blocked.
- MX Records: Perform an MX lookup to identify the recipient email provider and investigate deliverability issues.
Marketer view
Email marketer from Reddit r/emailmarketing suggests that the issue might be related to a recent campaign that triggered spam filters. They recommend segmenting your list and sending more targeted emails to improve engagement and avoid being flagged as a spammer. Also warming up your IP address if you are new to sending volume.
16 Jul 2022 - Reddit r/emailmarketing
Marketer view
Email marketer from StackExchange answers that a 'MailBlockKnownSpammer' error often means your IP or domain is on a Real-time Blackhole List (RBL). They suggest checking your IP against common RBLs using a tool like MultiRBL and taking steps to get delisted if necessary. Also monitor complaints.
10 Dec 2021 - StackExchange
What the experts say
2 expert opinions
The 'MailBlockKnownSpammer' bounce message indicates a block based on the sender's perceived reputation. Resolving this involves immediately checking your blocklist status and contacting the blocking entity (ISP or email provider) to request remediation, emphasizing your adherence to email best practices. Maintaining a consistent and positive sender reputation is vital, achieved through monitoring reputation using available tools, proactively addressing negative feedback, and ensuring clear communication with recipients about the purpose and value of your transactional messages.
Key opinions
- Reputation is Key: The MailBlockKnownSpammer error is a direct result of a negative sender reputation.
- Action Required: Proactive monitoring and addressing of reputation issues are crucial for maintaining transactional email deliverability.
- Communication Matters: Clear communication with recipients enhances trust and mitigates potential complaints.
Key considerations
- Check Blocklists: Immediately check your domain and IP against common blocklists.
- Contact Blocking Entity: Reach out to the blocking ISP or email provider to request delisting and explain your commitment to best practices.
- Monitor Reputation: Use available tools to consistently monitor your sender reputation.
- Address Feedback: Proactively address any negative feedback or complaints to improve your reputation.
- Communicate Clearly: Ensure clear communication with recipients regarding the purpose and value of your transactional messages.
Expert view
Expert from Spam Resource explains that the 'MailBlockKnownSpammer' message indicates a block based on the sender's perceived reputation. Immediate steps involve checking blocklist status and contacting the blocking entity (e.g., the specific ISP or email provider) for remediation, emphasizing adherence to best practices.
21 Feb 2022 - Spam Resource
Expert view
Expert from Word to the Wise emphasizes that consistent and positive sender reputation is vital for transactional email deliverability. She advises monitoring sender reputation using available tools, proactively addressing any negative feedback or complaints, and ensuring clear communication with recipients about the purpose and value of transactional messages.
9 Dec 2022 - Word to the Wise
What the documentation says
3 technical articles
Transactional emails bouncing with 'MailBlockKnownSpammer' are generally due to the receiving mail server identifying the sender as a source of unsolicited mail based on several factors. These include spam complaints, high bounce rates, detection of suspicious sending patterns, and poor sender reputation. To resolve this, it's essential to monitor IP reputation and subscriber complaints using tools like Microsoft's SNDS and JMRP, adhere to bulk sender guidelines from Gmail and other providers (including authentication and easy unsubscribe options), and investigate specific SMTP error codes in logs to understand the rejection reason.
Key findings
- Reputation Matters: Sender reputation is a critical factor in determining whether transactional emails are blocked.
- Multiple Factors at Play: Blocking decisions are based on a combination of signals, including spam complaints, bounce rates, and sending patterns.
- Guidelines are Key: Following bulk sender guidelines from major email providers is essential to avoid being marked as a spammer.
- Error Codes: SMTP error codes can provide insights into the specific reasons for email rejections.
Key considerations
- Monitor Reputation: Actively monitor IP reputation and subscriber complaints using available tools (e.g., SNDS, JMRP).
- Follow Guidelines: Adhere to bulk sender guidelines from major email providers like Gmail, Outlook.com, etc.
- Implement Authentication: Ensure proper email authentication (SPF, DKIM, DMARC) to verify sender identity.
- Provide Unsubscribe: Offer easy and accessible unsubscribe options to reduce spam complaints.
- Review Logs: Investigate SMTP error codes in email logs to understand the specific reasons for rejections and take appropriate action.
Technical article
Documentation from Google Postmaster Tools explains that Gmail uses various signals to identify spam, including user reports, engagement metrics, and sender reputation. To avoid being marked as a spammer, it is crucial to follow Gmail's bulk sender guidelines, which include authenticating emails, maintaining low spam complaint rates, and providing easy unsubscribe options.
13 Aug 2022 - Google Postmaster Tools
Technical article
Documentation from RFC Editor details that specific SMTP error codes related to blocking (though not explicitly 'MailBlockKnownSpammer') indicate a policy rejection by the receiving server. This means the server has a reason to refuse the message, whether it is due to sender reputation, content filtering, or other security measures. Review your logs to get the exact code that indicates the policy rejection.
27 May 2024 - RFC Editor
How can I resolve high bounce rates and 'mailbox unavailable' errors for a specific domain?
Why am I seeing bounce issues when my HTML is UTF-8 with copyright characters?
How are email bounce rates calculated and what is considered a good bounce rate?
How can I resolve Microsoft Outlook S3140 errors blocking my transactional emails?
Do I need DMARC for transactional emails from a small website, and what are the best low-cost alternatives for sending emails if my IP is blocked?
What causes '550 relaying denied' bounce errors and how to resolve them?
