If you have chosen one of the following options in the Settings button of your mailing 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 Members button, you will notice that a new column has appeared which is named Double opt-in and the email address has the status Not Verified.
There are different reasons why you may see this status.
i) The user has subscribed to your mailing list, but hasn't yet click on the verification link that was included in the confirmation email sent.
ii) You have manually imported the subscriber either via the add member or via the other import methods (CSC, Excel, Copy/ Paste) and since you don't have the consent via a Double Opt-in process, you haven't checked the checkbox.
In case you already have been given consent by other means, you may add members as verified by ticking the respective checkbox below. Else, the owners of imported addresses will receive an email to confirm their subscription consent.