What it does?
It allows people to unsubscribe to any email, it has a database of recipients who opted out, you will get a REJECT notification from postfix if you try to mail anyone in that list. Your mailserver prevents you from accidently contacting those who have opted out.
rubengerad/mailcow-unsub
I have a few domains and wanted to ensure that emails had proper unsubscribe feature, however, setting it up as an app seems an overkill so I decied to add a module mailcow-unsub which provides automated provisioning there are two final steps that you need to do manually and restart postfix and nginx for enabling one click unsubscibe feature. I have shared the repo. Hope this helps!