🚀 go-pugleaf

I have seen several user-extension fields that lack the "X-" prefix
(making them simply extension-fields; subject to being redefined)
in hopes that other sites might employ them.

  Since some extension fields (user or other) involved the processing
of incoming mail, it only makes sense for a site which supports such
fields to inform others so that the incoming mail it recieves may
contain such information.  If, for example, a mail system supported
field yyyyy, how would/could it tell other mail system programmers
about it?  Is any agent maintaining a lists of'commonly used rfc822
extension fields?

-- John Curran
-- Umass/Amherst