Let it be known: a message that ends up in the spam folder is a lost message. Among the most commonly used tools for filtering spam, SpamAssassin is one of the most widespread. It assigns a score to each email analyzed, thereby determining whether it is legitimate or should be considered as unwanted. In this article, we propose to break down the SpamAssassin score, understand how it works, and see how to optimize your emails to successfully pass spam filters.
What is SpamAssassin?
SpamAssassin is an open-source software developed by the Apache Software Foundation, designed to analyze incoming emails and assess their legitimacy. Thanks to a series of algorithms and advanced filters, it assigns a score based on various parameters to determine the likelihood that a message is spam.
This tool is widely used by mail servers to improve deliverability and block unwanted mail before it reaches users’ inboxes.
Understanding the SpamAssassin Score Functionality
SpamAssassin works by applying a set of rules to each received email. Each of these rules assigns a certain number of positive or negative points according to predefined criteria. The message is then compared to a threshold set by the mail server: if its score exceeds this threshold, it is marked as spam.
Analysis Methods Used by SpamAssassin
Email Header Analysis: Verification of the sender’s address, the presence of SPF, DKIM, and DMARC records, and identification of address spoofing attempts.
| Bayesian Filtering | Analysis based on words and phrases frequently associated with spam. |
| Blacklists | Verification of the sender’s IP address in databases listing addresses associated with spam. |
| Suspicious Link Detection | Identification of URLs redirecting to fraudulent or malicious sites. |
| Heuristic Analysis and Weighted Scoring | Assigning points based on the message structure, layout, attachments, and content. |
Scoring and Spam Thresholds
SpamAssassin evaluates each email and assigns it a score. The lower this score, the more likely the email is to reach the inbox. The standard value used is often set at 5, but it can be adjusted.
An email scored just below 5, like 4.5 or 4.9, does not necessarily end up in spam. As long as it remains below this threshold, it will likely be accepted. Conversely, an email above this limit is likely to be blocked and never reach its destination.
Administrators can customize this threshold according to their requirements, sometimes even below 4.0 to be stricter. Other spam filters may also be used, with their own criteria.
The goal remains clear: the lower the SpamAssassin score, the better the chances of arriving at the destination.
Factors Influencing the SpamAssassin Score
1. Issues Related to Headers and Authentication
Email authentication is a key technical element to reduce the SpamAssassin score. Poor configuration of SPF, DKIM, or DMARC can lead to a significant increase in the score.
2. Content and Layout
A poorly structured email or one with suspicious content can be quickly penalized and end up on the dark side of SpamAssassin.
Points to Check:
- Excessive use of commercial keywords: beware of terms like “free”, “special offer”, or “urgent” as they are detected and add points to the score.
- Poorly formatted HTML code: emails containing superfluous tags or incorrect encoding may be penalized.
- Unbalanced text/image ratio: an email containing only images without explanatory text is more likely to be marked as spam.
3. Presence of Suspicious Links and Attachments
The use of shortened links can significantly increase the score assigned by SpamAssassin, as they mask the final destination and are frequently used by spammers.
Multiple redirections also pose a problem because when a URL goes through several redirects before reaching its destination, it is perceived as suspicious by spam filters.
Finally, risky attachments, such as ZIP files, EXEs, and macros embedded in Word or Excel documents, are often associated with spam. These files can contain malicious code and are therefore closely scrutinized by filtering systems.
How to Optimize Emails to Reduce the SpamAssassin Score?
Technical Improvement of Headers and Authentication
- Correctly configure SPF, DKIM, and DMARC to validate the authenticity of emails.
- Ensure that the sending IP address is not listed on blacklists.
- Avoid using shared SMTP servers with a poor reputation.
Content Structuring and Optimization
- Moderate the use of keywords strongly associated with spam.
- Maintain a good balance between text and images to ensure good readability.
- Ensure that HTML code is clean and adheres to responsive design standards.
Testing and Validation Before Sending
Before launching a campaign, test your email with anti-spam diagnostic tools such as Mail-Tester, GlockApps, or Google Postmaster Tools.
In short, SpamAssassin only lets through the most impeccable emails. Understanding how it works ensures that your messages pass the steps unhindered to their final destination. By adjusting technical aspects like authentication and content structure, you give your messages every chance of landing in the right place.
