Contacts will have one of the following statuses.
Mailable: You can send emails to these contacts.
Unconfirmed: These contacts signed up for this list using a sign up form or landing page and haven't double opted-in yet. You cannot mail to these contacts.
On Hold: You have exceeded your account list size. These contacts cannot be mailed to until you upgrade your account.
Bounced: These contacts hard bounced. You cannot mail to these contacts.
Unsubscribed: These contacts clicked Unsubscribe in an email campaign or through their email provider. They cannot be mailed to.