Summary
Even with proper authentication (DMARC, DKIM, SPF), your IPs might be listed on Spamhaus CSS due to factors beyond technical setup. These include sending spam-like content (even if unintentionally), sudden volume spikes, negative recipient engagement (low open rates, high unsubscribe rates, spam complaints), poor domain reputation (resulting from complaint rates, engagement metrics, and spam trap hits), list hygiene problems, issues with hostname PTR records, sending to typo domains, or having accounts with domains listed on the DBL. If using shared IPs, the actions of other users can impact your reputation. Additionally, Spamhaus also tracks user engagement and may blacklist IPs based on low engagement or spam reports. A high bounce rate for OTP emails may indicate issues with opt-in practices.
Key findings
- Content Matters: Spam-like content, even if unintentional, can trigger listings despite authentication.
- Engagement is Crucial: Low open rates, high unsubscribe rates, and spam complaints negatively impact reputation.
- Reputation is King: Maintaining a good domain and IP reputation is critical for deliverability.
- Authentication Isn't Enough: DMARC, DKIM, and SPF are not guarantees; sender behavior and reputation are paramount.
- List Hygiene Matters: Sending to outdated, unclean, or typo-filled lists can lead to blacklisting.
- Shared IPs Carry Risk: On shared IPs, the actions of other users can affect your reputation.
- Spamhaus Tracks Users: Spamhaus tracks user behavior related to your emails.
- DBL Listings Hurt: Having accounts with domains listed on the DBL can contribute to listing issues.
- Bounce Rates as Indicators: High bounce rates, especially for transactional emails, signal list quality or opt-in problems.
Key considerations
- Audit Email Content: Routinely review your email content for spam triggers and improve formatting.
- Monitor Engagement: Closely monitor open rates, unsubscribe rates, and spam complaints.
- Clean Email Lists: Regularly clean your email lists to remove inactive, problematic, or typo-ridden addresses.
- Manage Reputation Proactively: Actively manage and monitor your domain and IP reputation.
- Implement Feedback Loops: Set up and monitor feedback loops to promptly address complaints.
- Regulate Sending Patterns: Avoid sudden and drastic spikes in sending volume.
- Block Typo Domains: Actively reject emails sent to common typo domains.
- Review User Behavior: Monitor user accounts, especially those exhibiting high bounce rates or sending suspect content.
- Address Customer Compliance: Establish and enforce strict policies to prevent customers from sending spam.
- Optimize PTR Records: Configure PTR records to clearly identify your servers as legitimate mail sources.
What email marketers say
12 marketer opinions
Even with proper authentication (DMARC, DKIM, SPF), your IPs might be listed on Spamhaus CSS due to factors beyond technical setup. These include sending spam-like content, sudden volume spikes, negative recipient engagement (low open rates, high unsubscribe rates, spam complaints), poor domain reputation (resulting from complaint rates, engagement metrics, and spam trap hits), list hygiene problems, shared IP reputation, or the content of emails containing 'spammy' words or poor formatting. Spamhaus also tracks user engagement and may blacklist IPs based on low engagement or spam reports.
Key opinions
- Content Matters: Spam-like content can trigger listings even with proper authentication.
- Engagement is Crucial: Low open rates, high unsubscribe rates, and spam complaints negatively impact reputation.
- Reputation is King: Maintaining a good domain and IP reputation is critical for deliverability.
- Beyond Authentication: DMARC, DKIM, and SPF are not enough; sender behavior and reputation are paramount.
- List Hygiene: Sending to outdated or unclean lists can lead to blacklisting.
- Shared Responsibility: On shared IPs, the actions of other users can affect your reputation.
- User Tracking: Spamhaus tracks user behaviors related to your emails.
- DBL Listed Domains: Accounts with domains listed on the DBL can contribute to listing issues.
Key considerations
- Content Audit: Review your email content for spam triggers and improve formatting.
- Engagement Monitoring: Monitor open rates, unsubscribe rates, and spam complaints.
- List Cleaning: Regularly clean your email lists to remove inactive or problematic addresses.
- Reputation Management: Actively manage and monitor your domain and IP reputation.
- Feedback Loops: Set up and monitor feedback loops to promptly address complaints.
- Sending Patterns: Avoid sudden spikes in sending volume.
- Reject Typo Domains: Reject emails sent to common typo domains.
- Review User Behavior: Monitor and address any toxic domains.
Marketer view
Email marketer from EmailToolTester shares that factors such as low engagement, spam complaints and spam trap hits can override authentication. Also highlights that even if your email passes authentication it will still be marked as spam.
3 May 2022 - EmailToolTester
Marketer view
Email marketer from SendGrid responds that being blacklisted despite proper authentication may point to issues beyond technical setup. They mention content issues, list hygiene problems, and low sender reputation as contributing factors, even when DMARC, DKIM, and SPF are correctly implemented.
26 Apr 2025 - SendGrid
What the experts say
7 expert opinions
Even with proper email authentication (DMARC, DKIM, and SPF), your IPs might be listed on Spamhaus CSS for several reasons. The content of your emails can trigger filters if it resembles spam, regardless of whether it actually is. High bounce rates, particularly for transactional emails, indicate issues with list quality or opt-in practices. Spam filters are designed to identify coordinated spamming attempts, meaning that reputation damage can spread across shared infrastructure. You should also monitor customer sending practices, as their behavior greatly influences your IP's reputation. Finally, also review your hostname PTR records to ensure they aren't triggering spam filters by looking like compromised servers.
Key opinions
- Content Matters: CSS listings are often triggered by content that resembles spam.
- Bounce Rates Indicate Problems: High bounce rates, especially for transactional emails, suggest issues with list quality.
- Shared Infrastructure Risks: Spam filters recognize coordinated attempts, so reputation damage spreads across shared IPs.
- Customer Behavior Impacts Reputation: The sending practices of your customers can significantly affect your IP's standing.
- PTR Records Influence Reputation: Improperly configured PTR records can make your servers appear compromised.
- Shared Responsibility: Other users behavior can impact your reputation if you are on a shared IP.
Key considerations
- Review Email Content: Audit your email content to avoid spam-like language and formatting.
- Improve List Hygiene: Ensure you are sending to opt-in addresses and implement bounce management.
- Monitor Shared Infrastructure: If on a shared IP, be aware of the sending practices of other users.
- Enforce Customer Compliance: Establish and enforce policies to prevent customers from sending spam.
- Optimize PTR Records: Configure PTR records to clearly identify your servers as legitimate mail sources.
Expert view
Expert from Email Geeks says to look at who the customers are, what mail they're sending and how they acquired the addresses. The behavior observed is typical of mail perceived as spam.
16 Aug 2022 - Email Geeks
Expert view
Expert from Email Geeks explains that spam filters are designed to recognize bad actors spreading traffic across multiple sources and that reputation damage can spread across shared infrastructure.
24 Mar 2025 - Email Geeks
What the documentation says
5 technical articles
Even with passing DMARC, DKIM, and SPF, your IPs can be listed on Spamhaus CSS because these authentication methods don't guarantee deliverability or prevent blacklisting. Spamhaus CSS focuses on characteristics similar to known spam sources, including spam content, spam trap hits, or malware distribution, regardless of authentication. Email blacklists consider factors beyond authentication, such as sending volume, complaint rates, and sender reputation. DMARC protects against direct domain spoofing but doesn't guarantee inbox placement. Maintaining a good domain reputation is important for avoiding junk folders.
Key findings
- CSS Focus: Spamhaus CSS identifies IPs exhibiting spam-like characteristics.
- Authentication Limitations: DMARC, DKIM, and SPF do not guarantee deliverability.
- Beyond Authentication Factors: Factors beyond authentication, like volume and complaint rates, matter.
- DMARC Scope: DMARC protects against spoofing, not all forms of abuse.
- Reputation Importance: Good domain reputation is important for inbox placement.
Key considerations
- Assess Content: Ensure your email content does not resemble spam.
- Monitor Sending Practices: Monitor sending volume, complaint rates, and spam trap hits.
- Manage Reputation: Actively manage your domain and IP reputation.
- Implement Feedback Loops: Use feedback loops to address recipient complaints.
- Review Security: Ensure your systems are not distributing malware.
Technical article
Documentation from RFC explains that while SPF prevents sender address forgery, it does not guarantee deliverability or prevent blacklisting. Blocklists like Spamhaus consider a wide variety of factors beyond the scope of SPF.
18 Aug 2024 - RFC
Technical article
Documentation from DigitalOcean explains that email blacklists, like Spamhaus, often consider factors beyond authentication, such as sending volume, complaint rates, and spam trap hits. Having correct authentication helps, but it's not the only determinant for avoiding blacklists.
22 Feb 2022 - DigitalOcean
Besides Spamhaus, what blocklists are important for email marketers to monitor?
How can I get delisted from Spamhaus?
How do DMARC, spam complaints, and IP reputation affect email deliverability and rejections?
How do I check Spamhaus for my IP address and understand the listings?
How do I get help with a Spamhaus CSS delist?
How do I prevent my IP address from being listed in the Spamhaus CSS database?
