Return content on non-delivery?

Applicable protocol:: Mail (http://www.rfc-editor.org/rfc/rfc2822.txt)
Status:: standards-track
Author/Change controller:: IETF (mailto:iesg@ietf.org)
Internet Engineering Task Force.
Specification document(s):: http://www.rfc-editor.org/rfc/rfc2156.txt
Related information:: Indicates whether the content of a message is to be returned with non-delivery notifications. Renamed version of obsolete Content-Return field. RFC 2156 (MIXER), not for general use.