rfc2822 April 2001

4.5.7. Obsolete trace fields

   The obs-return and obs-received are again given here as template
   definitions, just as return and received are in section 3.  Their
   full syntax is given in [RFC2821].

obs-return      =       "Return-Path" *WSP ":" path CRLF

obs-received    =       "Received" *WSP ":" name-val-list CRLF

obs-path        =       obs-angle-addr