Email notifications Unsubscribe link, Outlook doesn't know how to use the link

Summary

When we receive email notifications in Outlook 2017, a little "Unsubscribe" link is available - very handy. But Outlook can't currently do anything with the unsubscribe, as it apparently needs more information. A thread on Microsofts forums indicates that Outlook might need an email address instead. Return-Path also mentions the change in Outlook (to the current behaviour, it seems) in this blog post.

It is entirely possible this feature cannot work without an email server hooked in to Gitlab. In that case, should the List-Unsubscribe header even be set?

The link in the bottom of emails is enough for most cases, so leaving the List-Unsubscribe header out might remove the bar with the option in outlook (and thus the offer to mark as junk).

What is the current bug behavior?

Outlook informs me it cannot unsubscribe, offers me to mark the sender as junk-mail instead.

What is the expected correct behavior?

Outlook magically removes me from the given subscription.

Relevant logs and/or screenshots

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)