How does the opt-in form work for logged-in users?
When a user is logged in, their email address (and possibly name) is already on record, so we don't need to collect it again. The user will only see a subscribe button. The results of clicking the button vary based on the site configuration.
Not yet subscribed
If there are multiple lists to choose from, the new subscriber will receive an email prompting them to choose one. If just one list (probably new posts) is enabled, the new subscriber will receive a confirmation email for their subscription.
When already subscribed
The widget displays the current subscription information.