How to troubleshoot a SURBL or blocklist listing for shared email infrastructure?

Key findings

• Shared domain impact: A blocklist listing on a shared domain, such as a DKIM signing domain or a default 'view in browser' link, can affect multiple clients or campaigns using that infrastructure.
• SURBL focus: Unlike some IP-based blocklists, SURBLs primarily target URLs found within the email content or headers, making the content of your campaigns a critical factor. For more information, read our guide on email blocklists.
• URL types: Commonly problematic URLs on shared infrastructure include default 'view in browser' links, unsubscribe links, and click-tracking domains, especially if clients have not configured custom CNAMEs.
• Content is key: Spamhaus and other blocklists can be triggered by content issues, and for shared IPs, this means that even a single problematic campaign can lead to widespread deliverability issues. Twilio provides additional details on avoiding email blocklists.
• Authentication impact: While SURBLs focus on URLs, issues with shared DKIM signing domains (part of your email authentication) can also indicate a problem, as these domains are often tied to the sender's reputation.

Key considerations

• Identify the source: Pinpointing which specific client or campaign triggered the listing is crucial for resolution, especially with shared resources. Tools for blocklist monitoring can assist in this.
• Review shared URLs: Scrutinize all shared URLs, including hidden tracking links, to determine if any of them are associated with the blocklist entry.
• Client segmentation: Consider if clients using custom DKIM or other custom authentication are less likely to be the source of issues on a shared general domain.
• Proactive monitoring: Implement continuous monitoring of all shared sending domains and IPs to detect and address blocklist issues promptly before they escalate.
• Communication: Maintain clear communication channels with your ESP or mail server administrator, as they are often best equipped to help resolve blocklist issues on shared infrastructure.

Key opinions

• Shared domain vulnerability: Many marketers realize that shared domains, especially those used for DKIM signing or default tracking, are common culprits when a SURBL or other blocklist listing occurs.
• Collateral damage: A common frustration among marketers is that a single client's poor sending practices on shared infrastructure can lead to deliverability issues for all other clients using that same resource.
• URL focus: Marketers frequently acknowledge that SURBLs primarily focus on URLs embedded within email content, rather than just the sending IP, which shifts the focus of investigation.
• Detection challenges: Identifying the specific client or campaign responsible for a blocklist entry on shared infrastructure can be challenging, requiring careful log analysis and historical data.
• ESP role: Marketers often depend on their Email Service Provider (ESP) to manage and resolve shared IP or domain blocklistings, as the ESP controls the underlying infrastructure.

Key considerations

• Custom authentication: Marketers consider whether clients using their own custom DKIM or CNAMEs for tracking links might be exempt from issues on the provider's default shared domains.
• Content review: Regularly reviewing email content for all clients, especially those on shared infrastructure, is vital to ensure no malicious or spammy URLs are being sent. See our guide on why your emails are going to spam.
• Monitoring tools: Utilizing monitoring tools to track shared IP and domain blocklist status is crucial for early detection and rapid response.
• User education: Educating clients on best practices for list hygiene and content creation can significantly reduce the risk of blocklisting on shared resources.
• Delisting process: Understanding the specific delisting procedures for different blocklists (like SURBL or Spamhaus) is important, though often managed by the ESP for shared infrastructure.

Key opinions

• SURBL mechanism: Experts clarify that SURBLs are generally more focused on URLs in the email body content rather than just header URLs or sending IPs, though header URLs are still a possibility.
• Shared infrastructure risk: The consensus among experts is that shared domains, IPs, and default tracking links pose a higher risk, as abuse from one client can lead to broad blocklisting for the entire infrastructure.
• Proactive content scanning: Experts recommend implementing robust content and URL scanning mechanisms for all outgoing emails, especially on shared platforms, to catch problematic links before they cause issues.
• Abuse mitigation: Effective abuse detection and rapid mitigation strategies are crucial for shared infrastructures to prevent widespread blocklistings caused by compromised accounts or bad actors.
• Reputation management: Maintaining a strong overall sender reputation across all shared components (IPs, domains, URLs) is paramount to avoiding blocklists. Learn more about understanding your email domain reputation.

Key considerations

• Client vetting: Implementing strict client onboarding and monitoring processes can prevent bad actors from jeopardizing shared resources.
• URL tracking consistency: Ensure that all URL tracking and default links are consistently monitored and, where possible, customized by clients to avoid shared domain issues.
• Immediate remediation: Promptly identify and address the source of abuse or problematic content to initiate the delisting process swiftly, minimizing downtime for all users. Our blocklist checker can help.
• Policy enforcement: Strong terms of service and acceptable use policies for shared infrastructure are essential to deter problematic sending behavior.
• DNSBL selection: The eco Association of the Internet Industry suggests that mail server administrators should carefully select DNSBLs (DNS-based Blackhole Lists) to ensure effective and balanced spam filtering. You can learn more about selecting a DNSBL on their website.

Key findings

• SURBL definition: Documentation consistently defines SURBLs as lists of websites (URLs) found in unsolicited messages, differentiating them from blocklists that target sender IPs or domains.
• Impact of shared IPs: Official support articles often explain that if a shared IP is listed on a major blocklist (e.g., Spamhaus), the ESP is typically responsible for addressing the issue, highlighting the provider's role in shared infrastructure management.
• Ease of delisting: Some documentation notes that blocklists designed for ease of removal (easy-on, easy-off) can reduce false positives and enable quicker recovery for legitimate senders.
• DNSBL selection: Guidelines exist for mail server administrators on how to select appropriate DNSBLs for effective spam filtering, indicating the strategic importance of choosing the right blocklists.
• Shared URL risks: Technical guides often emphasize that shared domains used for tracking or image hosting can become blocklisted if abused, even if the primary sending IP remains clean.

Key considerations

• Regular audits: Documentation implies the need for regular audits of all URLs used within email campaigns sent via shared infrastructure, including those for tracking, images, and 'view in browser' links.
• Provider communication: Official support channels often suggest that direct communication with your email service provider is the most effective route for resolving shared IP or domain blocklistings. See how to resolve email IP blocks with Yahoo Mail.
• Content filtering: Implement or leverage automated content filtering and URL scanning on outgoing emails to prevent problematic links from being sent, especially in shared environments.
• Understanding listing criteria: Review the specific criteria for various blocklists (e.g., SURBL, Spamhaus) to understand what triggers a listing and how to avoid it in the future, particularly for shared resources.
• Client onboarding policies: Documentation from service providers implies the need for clear client onboarding policies and usage agreements to prevent misuse of shared infrastructure.