Inbox Preview's Spam Filter Checks sometimes provides additional feedback about why your test email did not pass certain spam filters. However, not all spam filters supply Return Path with information regarding what rules have been triggered in processing the email. These companies do not provide feedback in order to conceal their filtering methodology so that the knowledge cannot be exploited by spammers.
When a company does provide feedback, Inbox Preview displays whatever information has been provided by the spam filter and automatically includes it. This information can be helpful in troubleshooting issues your email is experiencing.