For me a protocol than can be use in any possible way you want is not a protocol because everybody would use it in a different way which = problems... - AS2 messages are always sent using the HTTP or HTTPS protocol (Secure Sockets Layer — also known as SSL — is implied by HTTPS) and usually use the "POST" method (use of "GET" is rare). - Messages can be signed, but do not have to be. - Messages can be encrypted, but do not have to be. - Messages may request a Message Disposition Notification (MDN) back if all went well, but do not have to request such a message.