Navigate SpamAssassin Filters with Ease

What SpamAssassin Is and Why It Matters

SpamAssassin is the most widely deployed open-source spam filtering platform in the world. It runs on mail servers globally and evaluates every incoming email against hundreds of rule checks, assigning a numerical score based on how many rules fire and how heavily each one is weighted. Emails that exceed the server's configured threshold — typically 5.0 — are routed to the spam folder or rejected entirely. Passing SpamAssassin is not optional for serious email senders.

How SpamAssassin Scoring Works

Every rule in SpamAssassin's ruleset carries a positive or negative point value. When a rule fires — meaning a condition in your email matches the rule's criteria — its points are added to or subtracted from your running total. Common rules include content-based checks for spam keyword density, HTML structure analysis, header validation, DNS lookup results, and Bayesian classifier output. Rules can also fire in combination, meaning two mild triggers together create a more severe penalty than either alone.

The Most Common Rules That Fire

HTML_MESSAGE is expected and low-scoring. MISSING_HEADERS fires when Date or Message-ID headers are absent. HTML_IMAGE_ONLY penalizes emails with too many images and too little text. BAYES_99 fires when the Bayesian classifier identifies your content as nearly certain spam based on learned patterns. RAZOR2 and PYZOR match your email's content fingerprint against databases of known spam. URI_PHISHING flags links that appear in phishing databases. Fixing these categories has the highest impact on score reduction.

HTML Structure and SpamAssassin

SpamAssassin analyzes the HTML structure of your email, not just the text content. Deeply nested tables, excessive use of font tags, JavaScript patterns, inline event handlers, and a high image-to-text ratio all contribute to score increases. Emails generated by visual builders often carry structural patterns that SpamAssassin penalizes — not because the content is spammy, but because the code resembles patterns associated with bulk spam campaigns. Clean, well-structured HTML produces lower scores.

How Campaign Cleaner Helps With SpamAssassin

Campaign Cleaner runs your email through SpamAssassin and returns a complete score report — every rule that fired, the points it contributed, and what triggered it. This gives you a prioritized action list: the highest-scoring rules to fix first. Campaign Cleaner also addresses the structural HTML issues that contribute to SpamAssassin scores by cleaning your code, optimizing your text-to-image ratio, and removing patterns that trigger content-based rules.