If you have double opt-in enabled then the subscriber's email address will only be passed to your preferred email marketing when they click the confirmation link.
The order of events is like this:
Subscriber opts-in to your form
Subscriber receives email asking them to confirm their email address
Subscriber clicks confirmation link
Subscriber’s email is passed to email integration
Subscriber is redirected to lead magnet
You can view the confirmation status of any subscriber via either the Lead Capture or Resource Library dashboards:
See the 'confirmed?' column for details:
