A New Internet-Draft is available from the on-line Internet-Drafts directories. This draft is a work item of the Internet Fax Working Group of the IETF.
A message originator sometimes sends content in a form the recipient cannot process. Such content needs to be converted to a related form, with the same or with restricted information, such as changing from color to black and white. In a store-and-forward environment, it can be convenient to have this conversion performed by an intermediary. This specification integrates two ESMTP extensions and three MIME content-types, to permit authorized, accountable content form conversion by intermediaries.
http://www.ietf.org/internet-drafts/draft-ietf-fax-esmtp-conneg-09.txt