If one of your Email Newsletter subscribers marks your newsletter as spam (whether intentionally or by mistake), the subscriber is removed from your 'Active' list.
They will be listed in your subscriber database in the Spam Reports section.
The good news is that this will not prevent you from from sending yourself a test of your newsletter draft nor from sending your newsletter to your active subscribers.
Also see this FAQ:
Newsletter Subscribers Screen - Explained
Our world-class customer care team is here for youContact Support