The spam score is evaluated using SpamAssassin filter which evaluates hundreds of parameters of your email - from header information to content and assigns each test a score which gives the overall score. Various aspects of the content are considered ranging from the subject, image to text ratio, words used to font sizes, etc. The score can have either negative or positive value - negative means your mail is unlikely to be marked as spam. Positive value increases the risk and values over 5 are considered a spam.
The results of the SPAM check are displayed at the campaign details page as an overall score. To see the individual tests that affected your score click Show details. We have color-coded the overall score for you to make it easy to understand. When your score is green, you are doing a great job. When you campaign's score is orange you we advise you to take a look at the details and evaluate the tests that penalize your campaign and try to reduce the score by adjusting the contents. If you are in the red you should seriously work on reducing the score.