Can anybody explain how Microsoft Outlook implement the unsubscribe button in the header

Hi nick_shore,

Microsoft Outlook, incorporates the unsubscribe button in the email header by identifying emails containing a "List-Unsubscribe" header in their metadata.

This header, usually included by the sender to adhere to anti-spam regulations and email marketing best practices, contains a URL or mailto link.Activating this link initiates an unsubscribe request to the sender's server.
Outlook recognizes this header, presenting users with a convenient "Unsubscribe" button as a quick link to this functionality.