OnINBOX intentionally does not scan emails that have been marked as spam, our view is that these emails should not be interacted with by users anyway. The primary purpose of OnINBOX is to provide security information on emails that have not been caught by other security measures (i.e. gateways and email spam folders). If an email has been marked as spam, there's generally a good reason for that and no need for OnINBOX to scan it a second time.
Email sent to your spam folder have already gone thought some sort of scanning and therefore bypass the OnINBOX scanning.
Written by Ivan KovachevUpdated over a week ago