If you have chosen one of the two following options in your List Settings:
i) Activate Double Opt-in for this list but continue sending to all subscribers
ii) Activate Double Opt-in for this list and only send to verified subscribers
Then, when you select the View list, you will notice that a new column has appeared named: Double opt-in and the email address has the status Verified (external).
That means that you have imported this user either manually or via our import features and you have checked and verified that this user has given you the consent to send him Email Marekting newsletters.