KOO is opt-in for each recipient. The recipient has to upload a key to KOO. Obviously, OpenPGP works differently from TLS, and TLS does not have a concept of k

KOO is opt-in for each recipient. The recipient has to upload a key to KOO. Obviously, OpenPGP works differently from TLS, and TLS does not have a concept of key servers - but key servers are absolutely not a new invention for OpenPGP, and it shouldn't be surprising that if you upload your key to one, you might get an encrypted email.