Similar to 'Sender:'

Applicable protocol:: Mail (http://www.rfc-editor.org/rfc/rfc2822.txt)
Status:: experimental
Author/Change controller:: Carl Malamud (mailto:carl@malamud.com)
Internet Multicasting Service.
Specification document(s):: http://www.rfc-editor.org/rfc/rfc1528.txt
Related information:: Sometimes used in Usenet News in similar ways to 'Sender:' Also used in printing protocols. Non-standard in Usenet News, Experimental in RFC 1528 (tcp.int).