Uh, well, in context of crypto - your (self-owned) crypto wallet totally would work. As for email... Sure, I guess it depends on the service and their policies

Uh, well, in context of crypto - your (self-owned) crypto wallet totally would work. As for email... Sure, I guess it depends on the service and their policies. But here's an anecdote. A few years ago, I've managed to log in in to a completely forgotten 10+ years old email account, finding its password in an old backup. It worked. ¯\(ツ)/¯ If an user cannot log in with a valid credentials, without brute-forcing them, after some years of absence, it's absolutely the service's fault. Of course, in the modern world, customer issues mean nothing so anything goes. But -quoting GP post - when designing a "fantasy football" alternate authentication system for the Internet, this probably shouldn't be a thing.