Currently when a user subscribe to an email topic. There is not way to take an action on them. It will be great to have an event to trigger when a user click the unsubscribe button on an email so we know and can take actions.

Example: User1 unsubscribe from clickfunnels email topic.

Info: User1 : Topic 1 unusbscribe

Then we can automate like tag user or send via webhook to third party email to unsubscribe.