There was the following comments about timelines. Those kinds of confirmation are not necessary over Internet-mail. There was an comment that all MTAs should be changed to configure it. This specification uses a post-hoc technique that permits an originator to send the best version known by the originator to be supported by the recipient and then sending a better version the recipient requests it. There are the following goals.
Sender selects alternative format based on receiver's capabilities.
Negotiation case example and optimized one were introduced. A question was raised about negotiation mechanism. Graham Klyne emphasized it is sender who judges the capabilities indicated by receiver and selects the format. He also notified the Receiver's state issue. This guide addresses implementations of the followings.