The User Preference Button is an Outpost-created feature that allows you to email subscribers and ask them to register a preference by clicking a button. When the user clicks the preference button in the email, we add a specified label to the user in Ghost.
So, for instance, if you wanted to ask your readers if they wanted and invitaiton to a special online event, when the user clicks the button, we would add the label "Special Online Event" in Ghost. You can then export all the email addresses of people with that label, and send them invitations.
There are also advanced uses you can make of this, such as adding an automation so that people who press that button are automatically subscribed to your podcast, or registered for an event. If you are interested in advanced uses like that, drop us a note at email@example.com.