return          =       "Return-Path:" path CRLF

path            =       ([CFWS] "<" ([CFWS] / addr-spec) ">" [CFWS]) /
                        obs-path

   Address to which notifications       Errors-To:,    Non-standard,
   are to be sent and a request to      Return-        discouraged.
   get delivery notifications.          Receipt-To:
   Internet standards recommend,
   however, the use of RCPT TO and
   Return-Path, not Errors-To, for
   where delivery notifications are
   to be sent.