How do spamassassin rules affect email deliverability?

However, SpamAssassin is still utilized by many smaller hosting providers (e.g., those using Plesk) and self-hosted email servers. Therefore, understanding its rules can still offer valuable insights into potential content or formatting issues that might trigger older or less advanced spam filters. Although a high SpamAssassin score might not directly block your emails at large providers, it can signal underlying problems that could indirectly affect your sender reputation and, by extension, your inbox placement. The focus for modern deliverability should be on maintaining a strong sender reputation and adhering to best practices, rather than solely optimizing for SpamAssassin scores.

Key findings

• Diminished Relevance: SpamAssassin's direct influence on deliverability for major mailbox providers is largely outdated; they use more advanced, holistic filtering systems.
• Rule-Based System: It assigns positive or negative scores based on content, headers, and sender characteristics. A score typically above 5 indicates spam. Learn more about understanding your SpamAssassin score.
• Custom Rules: Some SpamAssassin implementations use additional, aggressive custom rules, like KAM_ rules, which may not reflect mainstream spam filtering logic.
• Legacy Use: It is still used by self-hosted domains and smaller providers, so a periodic check can still be beneficial for broader compatibility.
• Insight, Not Decision: SpamAssassin scores can highlight problematic content or formatting but are not the primary determinant for major inbox placement outcomes today. For a deeper dive into what really impacts inbox placement, see our article on why SpamAssassin is not relevant for modern email deliverability.

Key considerations

• Focus on Reputation: Prioritize building and maintaining a strong sender reputation through consistent engagement, low bounce rates, and proper authentication (SPF, DKIM, DMARC).
• Content Quality: Even if SpamAssassin isn't a primary filter, its rules can sometimes indicate universally problematic content patterns, such as suspicious subject lines (e.g., those ending in numbers, often associated with malware), or certain top-level domains (TLDs) known for abuse. Check Spamhaus's list of most abused TLDs.
• Holistic View: Understand that modern spam filtering considers various factors including user complaints, spam trap hits, and authentication status. Review our guide on best practices for email deliverability.
• Test Periodically: Running tests against SpamAssassin, especially a stock version, can provide a secondary layer of content validation, even if it's not the primary filter for your recipients.

Key opinions

• Limited Impact: Marketers generally agree that mainstream mailbox providers do not primarily block emails based on simple SpamAssassin scores. Their filtering is more complex and holistic, considering sender reputation and engagement.
• Diagnostic Tool: SpamAssassin, particularly its custom rule sets, can still act as a trigger to re-evaluate subject line formats or domain choices that might appear suspicious, even if they don't lead to direct blocking.
• Self-Hosted Relevance: Some acknowledge that self-hosted domains using platforms like Plesk might still rely on SpamAssassin for filtering, making its scores relevant for a subset of recipients.
• Holistic Reputation: The greater concern for marketers is how content and sending practices contribute to overall sender reputation, which directly impacts deliverability across all providers. Learn more about what factors influence email deliverability.

Key considerations

• Subject Line Patterns: Even if a SpamAssassin rule (like numbers in subject lines) has a low score, it's worth reviewing if such patterns are associated with known spam or malware, as perceived by recipients or other filters. Avoid specific spam words and patterns that can trigger filters.
• TLD Sensitivity: Be mindful of Top-Level Domains (TLDs) that have a prevalent association with spam or malware, as this can affect filtering even if not directly flagged by SpamAssassin.
• Beyond Scoring: Instead of obsessing over specific SpamAssassin scores, focus on broader deliverability factors such as email list hygiene, engagement, and domain reputation. This broader approach is why your emails might still be going to spam.

Key opinions

• Outdated Relevance: Experts universally state that major mailbox providers no longer use SpamAssassin as a primary filter. Their systems are far more advanced and responsive to real-time threats.
• Holistic Filtering: Modern spam filters evaluate a multitude of signals, including sender reputation, engagement metrics (opens, clicks), complaints, spam trap hits, and authentication protocols (SPF, DKIM, DMARC), rather than static rules.
• Diagnostic Value: Despite its declining direct impact, SpamAssassin can still serve as a proxy tool to identify content or structural issues that might trigger other, more sophisticated filters or lead to poor user experience. See how Razor2 email scores offer similar diagnostic insights.
• TLD Risk Assessment: Certain TLDs are inherently riskier due to their historical association with abuse, and using them can increase scrutiny from various spam filters, not just SpamAssassin.

Key considerations

• Reputation is Key: Focus efforts on building and maintaining a pristine sender reputation. This involves consistent good sending practices, managing engagement, and avoiding spam traps. Understand the importance of spam traps.
• Content Quality: While SpamAssassin rules might highlight content issues, the broader goal is to create valuable, engaging content that recipients want to receive, reducing complaints and increasing positive engagement.
• Modern Authentication: Ensure your email authentication (SPF, DKIM, DMARC) is correctly configured and enforced, as this is a fundamental requirement for modern deliverability. Broken SPF records can significantly impact deliverability.

Key findings

• Scoring Mechanism: SpamAssassin processes emails by running various tests, each associated with a positive or negative score. The sum of these scores determines the email's overall spam likelihood. A score of 5 or higher often flags an email as spam by default, though thresholds can vary.
• Rule Categories: Rules cover various aspects like content, headers, DNS blacklists (blocklists), and specific phrases or patterns often found in spam. This can include issues like a high image to text ratio.
• Open-Source Nature: Being open-source, SpamAssassin can be customized with additional rules (e.g., KAM_ rules), which means its exact behavior can vary significantly between different implementations.
• Contextual Filtering: While SpamAssassin focuses on static rules, modern spam filtering, as described by deliverability documentation, increasingly uses contextual and behavioral analysis. This means an email's sender reputation, engagement, and authentication matter more than specific content flags.

Key considerations

• Rule Specificity: Understanding which specific SpamAssassin rules are triggered can provide granular insight into what aspects of your email content or structure might be perceived as spammy. This includes potential issues like malformed HTML.
• Thresholds: Be aware that the default spam threshold for SpamAssassin is typically 5, but some stricter systems may lower it to 4 or even higher. Knowing the recipient's system's threshold is crucial for self-hosted domains. This aligns with what is mentioned in documentation on SpamAssassin's default thresholds.
• Complementary Tool: View SpamAssassin as a tool for a specific type of spam filtering that complements, but does not replace, the more complex and dynamic systems used by major inbox providers. It’s one piece of the puzzle for understanding why emails might fail to reach the inbox.