displaying, on a display screen, the single message document according to a conversational view based upon a perspective of {HEAD ~ the response level} of {TAIL ~ a user} within the mail thread 
displaying , on a display screen , the single message document according to a conversational view based upon a perspective of { HEAD ~ the response level } of { TAIL ~ a user } within the mail thread
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH