SPAM Score Threshold is the upper limit beyond which the email is regarded as SPAM. The score must be below the permissible threshold to ensure the inbox deliverability of the email. An email with a SPAM Score more than 15 is considered to have high probability of landing into the SPAM folder. When you click "Publish to World" for such emails, you see the SPAM Score meter displaying the reasons of high SPAM score. Until you fix the reasons, you cannot publish the campaign.