%% You should probably cite rfc4141 instead of this I-D. @techreport{ietf-fax-esmtp-conneg-13, number = {draft-ietf-fax-esmtp-conneg-13}, type = {Internet-Draft}, institution = {Internet Engineering Task Force}, publisher = {Internet Engineering Task Force}, note = {Work in Progress}, url = {https://datatracker.ietf.org/doc/draft-ietf-fax-esmtp-conneg/13/}, author = {Dave Crocker and Kiyoshi Toyoda}, title = {{SMTP and MIME Extensions for Content Conversion}}, pagetotal = 26, year = 2005, month = jan, day = 21, abstract = {A message originator sometimes sends content in a form the recipient cannot process or would prefer not to process a form of lower quality than is preferred. Such content needs to be converted to an acceptable form, with the same information or constrained information (e.g., changing from color to black and white). In a store-and-forward environment, it may be convenient to have this conversion performed by an intermediary. This specification integrates two ESMTP extensions and three MIME content header fields, which defines a cooperative service that permits authorized, accountable content form conversion by intermediaries. {[}STANDARDS-TRACK{]}}, }