If you have chosen one of the following options in the Set your settings button of your email list:
i) Activate Double Opt-in for this list but continue sending to all subscribers (Soft Double Opt-in)
ii) Activate Double Opt-in for this list and only send to verified subscribers (Strong Double Opt-in)
Then, when you click on the View all members button, you will notice that a new column has appeared which is named Double opt-in and the email address has the status Verified by Admin.
This 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 marketing newsletters.