Corporate mail security scanners visit every link in an inbound email to check it is safe. A one-click unsubscribe link, visited by a scanner, unsubscribes the recipient — who never saw the email, never asked to opt out, and is now permanently unreachable.
This was silently shrinking reachable audiences for anyone emailing companies with mail security in place, which is most enterprises.
Unsubscribe now takes two steps: the link shows a confirmation page, and the opt-out is only processed when the person confirms it. Scanners fetch the page and stop there; humans click through in one extra second.
Genuine opt-outs still work exactly as before, and one-click list-unsubscribe headers are unaffected — those are handled by the mail client, not by link fetching.