Nope. From the article: "Once a client recognizes a contact as being fully e2e capable, it will not permit transmitting plaintext to that contact, even if that

Nope. From the article: "Once a client recognizes a contact as being fully e2e capable, it will not permit transmitting plaintext to that contact, even if that contact were to downgrade to a version of the software that is not fully e2e capable. This prevents the server or a network attacker from being able to perform a downgrade attack."