RFC 8058 uses a consented HTTPS POST for one-click unsubscribe, separating that request from automated link fetching.
Email scanners can fetch links before a reader acts. A distinct unsubscribe request lets receiving mail software act on consent without requiring another visit to the sender's website. For an implementation, test that fetching a link leaves subscription status unchanged and the authorized POST performs the unsubscribe.
Open question. This specification does not measure reductions in spam complaints or improvements in inbox placement. It leaves when and how consent is obtained outside its scope, and warns that someone with access to a message can unsubscribe its recipient. Correct behavior still needs testing in the actual mail system.
What changed in version 2
First editorial publication, checked against RFC 8058 sections 1, 3.2 and 6. January 2017 source; newly reviewed here.