​
Introduction

This block is caused by the subject score among other factors.

​
How Subject Scoring Works

Subject scoring is a common technique used in spam filters to evaluate the likelihood that an email is spam based on its subject line. Here’s how it typically works:
  1. Keyword analysis: The filter checks for spam-related keywords or phrases in the subject line.
  2. Pattern recognition: It looks for patterns commonly used in spam, such as excessive capitalization or special characters.
  3. Length consideration: Very short or excessively long subject lines may be flagged.
  4. Historical data: The filter compares the subject to a database of known spam subjects.
  5. Machine learning: Advanced filters use AI to adapt and improve detection over time.
If the subject line accumulates a high enough score based on these factors, it may trigger a block, resulting in the 550 [SS] error. To reduce the risk of subject-related blocks:
  • Use clear, relevant subject lines
  • Avoid spam-like phrases or excessive punctuation
  • Keep subjects concise but descriptive
  • Test subject lines with spam checking tools before sending