A New Internet-Draft is available from the on-line Internet-Drafts directories.
Abstract: “During the last few years, a number of proposals for extensions or improvements to email have run into trouble with a side-effect of mail relaying. In the current Internet Mail model, every SMTP server is required to break strict layering by inserting one or more additional “trace” headers into the message headers which are actually part of the SMTP payload. Since the headers are altered in transit, header-signing is not an available option, various anti-spam and internationalization strategies are infeasible or much more complex, and so on. This document proposes to change the Internet mail model to place the in-transit trace information in the envelope, removing the requirement that relaying systems modify the message payload.”
An interesting idea for sure, and one that could pave the way for some important future developments. Even so, I have to agree with the author that deciding if this is a good idea requires some hard thinking. From his announcement to the Internet Mail Consortium SMTP mailing list: “I am not at all convinced that it is a _good_ idea, only that, if we are talking about radical changes to the mail infrastructure to support various extended services, this is the sort of “clean up the warts that get in the way” option we might want to consider.”
Hector Santos is a man of many words, and had quite a bit to say on the matter.
http://www.ietf.org/internet-drafts/draft-klensin-email-envelope-00.txt