An unsubscribe is an operational state, not just a link click.
Record enough information to suppress future applicable sends even if a list is re-imported later. Define whether the request applies to one list, a category of mail, or all promotional mail according to the user’s choice and your legal/operational requirements.
Do not silently recreate subscriptions from stale CRM exports.
For automated one-click requests, validate the opaque token and process the request without requiring an interactive login.