Why is SpamAssassin not relevant for modern email deliverability and what truly impacts inbox placement?

Key findings

• Outdated Relevance: SpamAssassin is rarely used by major mailbox providers today. Its rule-based approach, focusing on keywords and content characteristics, does not align with modern, dynamic spam filtering methods.
• Shift to Reputation: Modern spam filters prioritize sender reputation and user engagement metrics, such as opens, clicks, and complaint rates, over static content analysis.
• Content's Evolving Role: Content still plays a role, but less in determining spam vs. inbox, and more in classifying email types (e.g., Gmail tabs for promotions vs. primary). Bad keywords, as identified by older tools, are largely irrelevant to modern filters.
• Authentication Importance: Email authentication protocols like DMARC, SPF, and DKIM are critical foundational elements for establishing trust and ensuring inbox placement.
• User Experience Focus: Mailbox providers heavily weigh how users interact with emails. Positive interactions (opens, replies) boost reputation, while negative ones (spam complaints, deletions without opening) severely damage it.
• List Management: Effective list hygiene and opt-in practices are paramount for maintaining good sender reputation. Avoiding spam traps and managing bounces are key indicators of a healthy sending program.

Key considerations

• Modern Filtering Mechanisms: Understand that major mailbox providers use highly advanced, dynamic filtering systems that learn from user interactions, not static rule sets. These systems continuously evolve to combat new spamming techniques.
• Focus on Reputation: Prioritize building and maintaining a strong sender reputation through consistent positive engagement and minimal negative feedback.
• Beyond Content: While good content is important for engagement, don't overemphasize keyword avoidance or image-to-text ratios based on outdated advice. Focus on providing value to your subscribers.
• Segment by Provider: Recognize that filtering mechanisms can vary between consumer providers (like Gmail, Outlook.com) and business filters. Business filters might still apply specific content rules based on internal company policies.
• Monitor and Adapt: Regularly monitor your deliverability performance using tools that provide insights into inbox placement across major providers, rather than relying on a single, outdated scoring system.

Key opinions

• SpamAssassin's Limited Utility: Many marketers continue to use SpamAssassin for pre-deployment checks due to past effectiveness, particularly for identifying trigger words in sensitive niches like finance.
• Keyword Obsolescence: There's a growing understanding that "bad keywords" and image/text ratios, once critical, are largely ignored by modern spam filters.
• Reputation is Key: Marketers are increasingly recognizing that sender reputation and how users interact with emails are the dominant factors in deliverability.
• Content for Classification: Content still helps providers like Gmail categorize emails into tabs (e.g., primary, promotions) rather than solely flagging them as spam.
• Learning Curve: Many marketers are in the process of adapting their strategies away from content-centric filtering models towards a more holistic understanding of inbox placement factors.

Key considerations

• Outdated Practices: Rethink the value of tools like SpamAssassin for modern deliverability testing. While they don't hurt, they don't provide a complete picture for consumer mailbox providers.
• Focus on Engagement: Prioritize strategies that foster positive user engagement, such as sending to highly engaged lists, personalizing content, and providing clear value.
• Authentication Compliance: Ensure proper email authentication setup, including SPF, DKIM, and DMARC, as these are non-negotiable for major providers.
• List Quality: Invest in maintaining a clean and engaged email list. High bounce rates and spam complaints are direct signals of poor list hygiene and severely impact reputation. Read more about email deliverability best practices.
• Holistic View: Understand that deliverability is a complex interplay of many factors, not just content. A holistic approach focusing on sender reputation, engagement, and technical setup is essential.

Key opinions

• SpamAssassin Obsolescence: Experts state that almost nobody uses SpamAssassin in its original form, especially for large-scale consumer email providers. Any remnants are in niche B2B appliances with diverged rules.
• No "Bad Keywords": Modern spam filters do not penalize emails based on "bad keywords" or simple content flags. Content is used for classification (e.g., promotional tabs), not for determining spam.
• User Experience Dominates: Major providers primarily care about user experience, with success at these providers largely dependent on how users interact with emails and the sender's list practices.
• Reputation, Not Just Sender: Deliverability is driven by reputation, but it's not solely the sender's reputation. It also involves the reputation of the content being sent, especially if similar content has been poorly received by other recipients.
• List Practices are Key: Improvements in inbox placement at major providers are often seen when senders improve their list and opt-in practices, rather than by adjusting content filters.
• Business vs. Consumer Filters: While consumer mailbox providers focus on reputation, business filters might have specific internal rules that block certain content regardless of sender reputation.

Key considerations

• Understand Modern Filtering: Recognize that the primary drivers of inbox placement are dynamic reputation signals, including user engagement, bounces, and spam trap hits, not static content rules.
• Prioritize User Interactions: Focus efforts on optimizing user experience and list practices to encourage positive engagement and minimize complaints. This is crucial for maintaining a good sender score and domain reputation.
• Beyond Content-Centric Testing: While pre-flight checks for obvious problems don't hurt, don't rely solely on tools like SpamAssassin. Instead, understand what specific rules mean and whether they are relevant to your target recipients. You can learn more about this in email deliverability myths.
• Reputation is Nuanced: Recognize that "reputation" extends beyond just your sending IP or domain. It encompasses the perceived reputation of your content itself based on how similar content has been received by others.
• Targeted Deliverability: Acknowledge that deliverability strategies may need to be adjusted based on the specific mailbox provider (consumer vs. business) you are targeting, as their filtering logic can differ significantly.

Key findings

• Evolution of Filtering: Modern email filters have evolved beyond static content analysis, now employing complex algorithms that factor in sender behavior, recipient feedback, and authentication.
• Authentication Mandate: Recent updates from major mailbox providers necessitate strict adherence to email authentication standards for successful inbox placement, making these protocols a baseline requirement.
• Engagement as a Metric: High levels of positive user engagement (opens, clicks, replies) are consistently shown to improve sender reputation, while negative engagement (spam complaints, non-opens) damages it.
• Content for Categorization: Email content's primary role is now often in classifying the message type (e.g., marketing, transactional, personal) for inbox sorting, rather than for direct spam flagging based on keywords.
• List Hygiene Criticality: Maintaining a clean, opted-in email list is highlighted as crucial, as bounces and spam trap hits severely impact sender reputation and lead to blocklisting.

Key considerations

• Compliance First: Prioritize compliance with sender requirements from major ISPs, especially new authentication and one-click unsubscribe mandates. These are now foundational for deliverability.
• Holistic Strategy: Adopt a comprehensive deliverability strategy that integrates strong sender reputation, consistent positive engagement, rigorous list management, and proper technical setup.
• Sender Reputation Monitoring: Actively monitor your sender reputation and inbox placement across key providers. This provides real-time insights into deliverability performance. Learn how SenderScore works.
• Adapt to New Rules: Stay informed about evolving deliverability trends and rules, such as those announced by Microsoft or Gmail, to ensure ongoing inbox success. Email deliverability in 2025 demands higher standards.
• Engagement-Driven Content: Craft compelling and relevant content that encourages positive user engagement, rather than obsessing over spam trigger words.