While RFC 2369 doesn't explicitly prioritize the order of MAILTO and HTTPS in the List-Unsubscribe header, the consensus from experts, marketers, and subsequent documentation (RFC 8058, M3AAWG) leans towards prioritizing HTTPS for its one-click unsubscribe functionality and better user experience. Technically, the order of preference is from first to last, but mailbox providers can reorder based on preferred protocols. Older tests showed that placing MAILTO first could negatively impact RFC8058 unsubs with certain providers. Ultimately, making unsubscribe as clear and easy as possible is key for compliance, sender reputation, and reducing spam complaints.