trace = [return]
1*received
return = “Return-Path:” path CRLF
path = ([CFWS] “<” ([CFWS] / addr-spec) “>” [CFWS]) /
obs-path
received = “Received:” name-val-list “;” date-time CRLF
name-val-list = [CFWS] [name-val-pair *(CFWS name-val-pair)]
name-val-pair = item-name CFWS item-value
item-name = ALPHA *([“-”] (ALPHA / DIGIT))
item-value = 1*angle-addr / addr-spec /
atom / domain / msg-id