E-mail is very far from secure. The overwhelming recommendation for private 1:1 communication is "use WhatsApp or Signal". But you're right that a federated and

E-mail is very far from secure. The overwhelming recommendation for private 1:1 communication is "use WhatsApp or Signal". But you're right that a federated and private 1:1 platform is possible /in theory/. However Facebook, a 1:many communication platform, is likely impossible to federate while retaining privacy.